ALBERT

Description: Recent geological and geophysical surveys in the Izu-Bonin-Mariana forearc have revealed the occurrence on the seafloor of oceanic crust generated in the initial stages of subduction and the earliest stage of island arc formation. The earliest magmatism after subduction initiation generated forearc basalts, and subsequently, boninitic and tholeiitic to calc-alkaline lavas were produced. Collectively, these rocks make up the extrusive sequence of the Izu-Bonin-Mariana forearc oceanic crust. This volcanic stratigraphy and its time-progressive development are analogous to those documented from many suprasubduction zone ophiolites. Most suprasubduction zone ophiolites may be on-land fragments of forearc oceanic crust, produced during the initiation of subduction and the early stages of island arc development.

Description: Volcanic glass from pillow lavas and hyaloclastites displays distinctive alteration textures that suggest the activity of boring microbes. Analogous textures are common in volcanic sections of the seafloor, in ophiolites, and in greenstone belts up to 3.5 Ga in age. While the origin of such trace fossils remains poorly understood, they offer much potential for investigating processes in the present-day, deep-ocean, crustal biosphere and their role in biogeochemical cycles.

Description: Much of our understanding of ocean ridges has come from the collection and analysis of glasses recovered from ridge axes. However, applying the resulting methodologies to ophiolite complexes is not straightforward because ophiolites typically experience intense alteration during their passage from ridge to subduction zone to mountain belt. Instead, immobile element proxies for fractionation indices, alkalinity, mantle temperature, mantle flow and subduction addition may be used to classify ophiolite lavas and fingerprint the precise setting of the ridge at which an ophiolite formed. The results can help us recognise and interpret past spreading centres and so make plate tectonic reconstructions.

Description: Ophiolites are suites of temporally and spatially associated ultramafic, mafic, and felsic rocks that are interpreted to be remnants of ancient oceanic crust and upper mantle. Ophiolites show significant variations in their internal structure, geochemical fingerprints, and emplacement mechanisms. These differences are controlled by (1) the proximity, when formed at the magmatic stage, to a plume or trench; (2) the rate, geometry, and nature of ocean-ridge spreading; (3) mantle composition, temperature, and fertility; and (4) the availability of fluids. The oceanic crust preserved in ophiolites may form in any tectonic setting during the evolution of ocean basins, from the rift–drift and seafloor spreading stages to subduction initiation and terminal closure. An ophiolite is emplaced either from downgoing oceanic lithosphere via subduction-accretion or from the upper plate in a subduction zone through trench–continent collision. Subduction zone tectonics is thus the most important factor in the igneous evolution of ophiolites and their emplacement into continental margins.

Description: Ophiolites are a newly documented host of diamonds on Earth. Abundant diamonds have indeed been separated from peridotites and chromitites of ophiolites in China, Myanmar, and Russia. In addition, diamond grains have recently been discovered in chromite from the Cretaceous Luobusa ophiolite (Tibet) and the early Paleozoic Ray-Iz ophiolite (polar Urals, Russia). These diamonds are accompanied by a wide range of highly reduced minerals, such as Ni–Mn–Co alloys, Fe–Si and Fe–C phases, and moissanite (SiC); these have been found as either mineral separates or inclusions in diamonds and indicate growth under superreducing conditions. The diamond-bearing chromite grains likely formed near the mantle transition zone and were then brought to shallow levels in the upper mantle to form podiform chromitites in oceanic lithosphere. Because these diamond grains occur widely in peridotites and chromitites of many ophiolites, we refer to them as ophiolite-hosted diamonds. It is possible that such diamonds may be common in the upper oceanic mantle.

Description: This chapter reviews detection of materials on solid and liquid (lakes and ocean) surfaces in the solar system using ultraviolet to infrared spectroscopy from space, or near space (high altitude aircraft on the Earth), or in the case of remote objects, earth-based and earth-orbiting telescopes. Point spectrometers and imaging spectrometers have been probing the surfaces of our solar system for decades. Spacecraft carrying imaging spectrometers are currently in orbit around Mercury, Venus, Earth, Mars, and Saturn, and systems have recently visited Jupiter, comets, asteroids, and one spectrometer-carrying spacecraft is on its way to Pluto. Together these systems are providing a wealth of data that will enable a better understanding of the composition of condensed matter bodies in the solar system. Minerals, ices, liquids, and other materials have been detected and mapped on the Earth and all planets and/or their satellites where the surface can be observed from space, with the exception of Venus whose thick atmosphere limits surface observation. Basaltic minerals (e.g., pyroxene and olivine) have been detected with spectroscopy on the Earth, Moon, Mars and some asteroids. The greatest mineralogic diversity seen from space is observed on the Earth and Mars. The Earth, with oceans, active tectonic and hydrologic cycles, and biological processes, displays the greatest material diversity including the detection of amorphous and crystalline inorganic materials, organic compounds, water and water ice. Water ice is a very common mineral throughout the Solar System and has been unambiguously detected or inferred in every planet and/or their moon(s) where good spectroscopic data has been obtained. In addition to water ice, other molecular solids have been observed in the solar system using spectroscopic methods. Solid carbon dioxide is found on all systems beyond the Earth except Pluto, although CO 2 sometimes appears to be trapped in other solids rather than as an ice on some objects. The largest deposits of carbon dioxide ice are found on Mars. Sulfur dioxide ice is found in the Jupiter system. Nitrogen and methane ices are common beyond the Uranian system. Saturn’s moon Titan probably has the most complex active extra-terrestrial surface chemistry involving organic compounds. Some of the observed or inferred compounds include ices of benzene (C 6 H 6 ), cyanoacetylene (HC 3 N), toluene (C 7 H 8 ), cyanogen (C 2 N 2 ), acetonitrile (CH 3 CN), water (H 2 O), carbon dioxide (CO 2 ), and ammonia (NH 3 ). Confirming compounds on Titan is hampered by its thick smoggy atmosphere, where in relative terms the atmospheric interferences that hamper surface characterization lie between that of Venus and Earth. In this chapter we exclude discussion of the planets Jupiter, Saturn, Uranus, and Neptune because their thick atmospheres preclude observing the surface, even if surfaces exist. However, we do discuss spectroscopic observations on a number of the extra-terrestrial satellite bodies. Ammonia was predicted on many icy moons but is notably absent among the definitively detected ices with possible exceptions on Charon and possible trace amounts on some of the Saturnian satellites. Comets, storehouses of many compounds that could exist as ices in their nuclei, have only had small amounts of water ice definitively detected on their surfaces from spectroscopy. Only two asteroids have had a direct detection of surface water ice, although its presence can be inferred in others.

Description: The injection of carbon dioxide into methane hydrate-bearing sediments causes the release of methane and the formation of carbon dioxide hydrate. This phenomenon known as CH 4 -CO 2 replacement creates a unique opportunity to recover an energy resource, methane, while entrapping a greenhouse gas, carbon dioxide. The paper "A comparative analysis of the mechanical behavior of carbon dioxide and methane hydrate-bearing sediments" by Hyodo et al. (2014) investigates stress-strain curves, shear strengths, and the effects of hydrate saturation, effective stress, and temperature on the mechanical behaviors of hydrate-bearing sediments that allow us to assessing the feasibility of CH 4 -CO 2 replacement method.

Description: A natural yellow and transparent crystal of Mn-bearing, Mg-rich gahnite (ZnAl 2 O 4 ) from Nordmark (Sweden) was studied by electron microprobe, single-crystal X-ray diffraction and optical absorption spectroscopy. The empirical structural formula of the crystal, T (Zn 0.52 Mg 0.34 Mn 2+ 0.08 Al 0.06 ) 1.00 M (Al 1.88 Mn 3+ 0.06 Fe 3+ 0.01 Mg 0.04 Mn 2+ 0.01 ) 2.00 O 4 , shows that Mn 2+ and Mn 3+ are almost completely ordered at the T and M sites, respectively. The electronic absorption spectrum of the spinel shows, in addition to a strong UV-absorption edge (O 2– -Mn 3+ and O 2– -Fe 3+ ligand-metal charge transfers) and two broad VI Mn 3+ -bands, a set of relatively narrow absorption bands at energies comparable to those caused by spin-forbidden electron transitions in tetrahedrally coordinated Mn 2+ in oxide spinel. However, the set of bands in the present spectrum is shifted to lower energies and they are intensified by approximately an order of magnitude compared to those recorded for spin-forbidden IV Mn 2+ -bands in spinel. These characteristic differences in combination with the determined cation distribution in the present gahnite demonstrates that electronic transitions in exchange coupled IV Mn 2+ – VI Mn 3+ pairs cause its color.

Description: The sulfate-bearing strata on Mars must have recorded rich information of its aqueous history. However, the hydrated sulfates observed in the surface thin layer by remote sensing, especially widespread kieserite, are likely weathering products rather than pristine deposits. Here we report the results from mineralogical investigations and environmental monitoring on the sulfate-bearing Dalangtan Playa (an analog site with Mars-like environmental conditions in northern Tibetan Plateau) to examine the depositional and secondary processes of hydrated sulfates. The regional deposition characters of DLT Playa were described based on our mineralogical results. Widespread kieserite was identified in situ by portable laser Raman spectrometer on the weathered surface of the Mg-sulfates-rich section, which formed from the hexahydrite dehydration after exposed to the ambient conditions in six months covering the summer, and survived in the winter. During summer days, wind and sunlight may have facilitated the dehydration process, leading the formation of kieserite from dehydration. On the basis of the observed kieserite formation, the recorded local environment conditions, as well as previously reported phase diagrams for Mg-sulfates, we suggest that the current diurnal relative humidity-temperature circles at low latitudes of Mars favor the formation of kieserite through secondary processes.

Description: A single-crystal neutron diffraction study of a synthetic ulvöspinel sample of composition Fe 3+ 0.40 Fe 2+ 1.80 Ti 0.80 O 4 was performed to investigate the static positional disorder at the octahedrally coordinated M site. Anisotropic structural refinement was performed in the space group Fd m against neutron Laue diffraction data collected at 298 K from two millimetric-sized crystals. Initial structure refinements were conducted with Fe and Ti sharing the M site (at 1/2, 1/2, 1/2), and their partial site occupancy was refined. The tetrahedrally coordinated T site (at 1/8, 1/8, 1/8) was modeled as fully occupied by Fe. For both crystals, the final R 1 index was about 3% for 9 refined parameters and 129 unique reflections, with no significant residuals. As the atomic displacement factors obtained were anomalously high, according to the previous experimental findings, F obs - and ( F obs – F cal )-difference Fourier maps of the nuclear density were generated. Fourier maps showed a significant minimum located out-of-center of the M site, and indicating a displacement of the Ti 4+ from the center of the octahedron. A further test refinement was successfully conducted with two mutually exclusive sites: M Ti out-of-center (at 0.49, 0.49, 0.49) and M Fe on the center (at 1/2, 1/2, 1/2). The resulting displacement of Ti from the octahedral center appears to be shorter than 0.15 Å. Using bond-valence theory, the out-of-center distortion of M Ti 4+ is interpreted as a result of intrinsic distortions in the ulvöspinel structure. The potential implication of the octahedral distortion on the behavior of ulvöspinel at non-ambient conditions is discussed.

Description: A suite of Hawaiian basalts that were variably altered in the presence of SO 2 -rich gases during the current summit eruptive episode at Halemaumau crater, Kilauea, were studied to determine their alteration phase assemblage and reactive pathways using electron microscopy, Mössbauer spectroscopy, and X-ray diffraction. The alteration conditions represent an acid fog environment. Alteration rinds on the basalts vary in thickness from tens of micrometers to the entirety of the rock and are composed of amorphous silica rims (85–95 wt% SiO 2 ) overlain by sulfates. Sulfate mineralogy consisted of gypsum, anhydrite, and natroalunite-jarosite. No phyllosilicates were observed in any alteration assemblages. Phenocrysts and glass were both observed to be extensively reacted during alteration. The Halemaumau samples may provide good analogs for basalt alteration on other rocky planetary bodies, i.e., Mars, Venus, and Mercury, where S is ubiquitous and low fluid/rock ratios are common.

Description: The nature of the fluorescence in the frequency-shift range of 1000–2500 cm –1 observed in the Raman spectra of many minerals when excited by a 785 nm laser has been investigated. Among the trivalent rare earths only Nd 3+ has the combination of a good ionic-radius match to substitute for Ca 2+ and an arrangement of energy levels to produce fluorescence in the frequency-shift range of interest. Raman/fluorescence spectra of six calcium-based minerals, namely fluorite, calcite, powellite, scheelite, apatite, and grossular/tsavorite, have been obtained at both room temperature and liquid-nitrogen temperature and transition assignments made for the majority of fluorescence lines in fluorite, powellite, scheelite, and grossular/tsavorite. The room-temperature results agree closely with results on individual minerals obtained by previous workers for fluorite and scheelite. The liquid-nitrogen-temperature results as well as the transition assignments for powellite and grossular/tsavorite are new. The Nd concentration has been measured by laser-ablation induction-coupled-plasma mass spectrometry (LA-ICP-MS) and correlated with Nd 3+ fluorescence intensity where possible. For fluorite, the fluorescence intensity increases at least linearly with concentration at levels up to a few parts per million and then saturates at higher levels due to concentration quenching. Analysis of room-temperature Raman/fluorescence spectra of a much larger group of minerals available on the RRUFF web site shows that strong or very strong Nd 3+ fluorescence is much more likely in calcium-based minerals than in non-calcium-based ones and is completely absent for minerals containing iron in the chemical formula. Nd 3+ fluorescence is best understood in fluorite and less well understood in the other five minerals. Further study of calcite, apatite, and grossular/tsavorite is necessary to improve the understanding of the charge-compensation mechanisms and increase the number of identified transitions in calcite and apatite. The results of this work indicate that Nd 3+ fluorescence in calcium-based minerals, when excited by a 785 nm laser, has potential uses in three areas: mineral identification, structure characterization and determination of trace-element concentration.

Description: We present an X-ray diffraction and multi-nuclear ( 2 H and 43 Ca) NMR study of Ca-exchanged hectorite (a smectite clay) that provides important new insight into molecular behavior at the smectite-H 2 O interface. Variable-temperature 43 Ca MAS NMR and controlled humidity XRD indicate that Ca 2+ occurs as proximity-restricted outer-sphere hydration complexes between –120 and +25 °C in a two-layer hydrate and at T ≤ –50 °C in a 2:1 water/solid paste. Changes in the 43 Ca NMR peak width and position with temperature are more consistent with diffusion-related processes than with dynamics involving metal-surface interactions such as site exchange. The 2 H NMR signal between –50 and +25 °C for a two-layer hydrate of Ca-hectorite is similar to that of Na- and other alkali metal hectorites and represents 2 H 2 O molecules experiencing anisotropic motion describable using the 2 H C 2 /C 3 jump model we proposed previously. 2 H T 1 relaxation results for Ca- and Na-hectorite are well fit with a fast-exchange limit, rotational diffusion model for 2 H 2 O dynamics, yielding GHz-scale rotational reorientation rates compatible with the C 3 component of the C 2 /C 3 hopping model. The apparent activation energy for 2 H 2 O rotational diffusion in the two-layer hydrate is greater for Ca-hectorite than Na-hectorite (25.1 vs. 21.1 kJ/mol), consistent with the greater affinity of Ca 2+ for H 2 O. The results support the general principle that the dynamic mechanisms of proximity-restricted H 2 O are only weakly influenced by the cation in alkali metal and alkaline earth metal smectites and provide critical evidence that the NMR resonances of charge-balancing cations in smectites become increasingly influenced by diffusion-like dynamic processes at low temperatures as the charge density of the unhydrated cation increases.

Description: Scheelite is well developed in hydrothermal deposits, providing a window into genetic processes and facilitating comparative studies, however, few studies have focused on characterizing scheelite in skarn-type W-Mo deposits. The primary ore mineral in the Jitoushan and Baizhangyan skarn-type W-Mo deposits (Anhui Province, Eastern China), scheelite was analyzed for major, trace, and rare earth element (REE) abundance and for Sr-Nd isotopes. The analysis revealed two unique geochemical characteristics that distinguish the scheelite from skarn-type W-Mo deposits to that from vein-type Au-W and porphyry-type W-Mo deposits: higher Mo content with a negative correlation between MoO 3 and WO 3 and a strong HREE depletion. Skarn-type scheelite mainly inherited REE signatures from ore-forming fluids, and the early precipitation of skarn minerals (e.g., garnet, diopside, and amphibole) has most likely resulted in the observed strong HREE depletion in scheelite and the decoupling of LREEs and HREEs. Of the numerous substitution mechanisms suggested by previous workers, 3Ca 2+ = 2REE 3+ + Ca (where Ca is a Ca-site vacancy) is preferred for the substitution of REE 3+ for Ca 2+ and in this study, particularly given the low salinity of ore fluids. As the scheelite Eu anomalies were inherited from ore-forming fluids with variable redox conditions and pH, the complex dEu/Mo correlation indicates that Mo increasingly entered the scheelite under oxidizing conditions and reached a maxim at dEu values of 0.8 to 1. In contrast, under reducing conditions, Mo contents in scheelite decrease gradually and Mo is precipitated as molybdenite as a result of the change in dominant valence state. Unlike the Sr-Nd isotope compositions of scheelite from vein-type Au-(W) and W-(Sb-Au) deposits, the scheelite from skarn-type W-Mo deposits has low ( 143 Nd/ 144 Nd)(t) (most 〈0.5125) and intermediate ( 87 Sr/ 86 Sr)(t) values (most between 0.708 and 0.715). The eNd(t) values of the scheelite varied from –16 to –12.3 in the Baizhangyan deposit and from –9.5 to –9.1 in the Jitoushan deposit, indicating that the ore-forming materials in the two W-Mo deposits were mainly derived from crustal sources.

Description: The crystal structure of the lead uranyl-carbonate mineral widenmannite has been solved from precession electron-diffraction data and refined using both electron-diffraction data and synchrotron powder-diffraction data. Widenmannite is orthorhombic, Pmmn , with a = 4.9744(9), b = 9.3816(16), c = 8.9539(15) Å, and V = 417.86(12) Å 3 . The structure was solved by charge-flipping and refined to an R 1 = 0.1911 on the basis of 301 unique, observed reflections from electron diffraction data, and to R p of 0.0253 and R F of 0.0164 from X-ray powder data. The idealized structure formula of widenmannite is Pb 2 (OH) 2 [(UO 2 )(CO 3 ) 2 ], Z = 2. However, both data sets suggest that the widenmmanite structure is not that simple. There are two symmetrically independent, partly occupied U sites. The substitution mechanism can be written as U(1)O 2 + Pb(OH) 2 U(2)O 2 . When the U(2) site is occupied, the U(1)O 2 group is absent, the two OH groups are substituted by O 2– and one Pb 2+ -vacancy. The chemical formula of the real structure should be written as Pb 2– x (OH) 2–2 x [(UO 2 )(CO 3 ) 2 ], where x is the probability of the substitution U(2) -〉 U(1). The probability of occurrence of U(2) refines to x = 0.074(15) from the powder-diffraction data and to x = 0.176(4) from the electron-diffraction data. There is one Pb site (nearly fully occupied), which is coordinated by 11 anions (up to the distance of 3.5 Å), including O and OH – . The shorter Pb-O bonds form a sheet structure, which is linked by the weaker bonds to the uranyl-carbonate chains to form a three-dimensional framework structure.

Description: We systematically investigated the L -edge X-ray emission spectroscopy (XES), a 3 d -to-2 p transition, of Fe 2+ - and Fe 3+ -bearing MgSiO 3 perovskite under high pressure based on the internally consistent LSDA+ U technique combined with the Slater-transition method. The Fe L -edge XES spectra can be used to directly interpolate the distribution of Fe-3 d electrons including the spin states and coordination environments of iron. Our results show that the spin transition from the high-spin state to low-spin state of Fe 2+ and Fe 3+ can be identified easily by the L -edge XES technique. The valence state of Fe (2+ or 3+) can be verified by this, since a shift of the first main peak of Fe 2+ across the spin transition of 2 eV, in good agreement with the experimental value (~1.6 eV), is significantly smaller than that of Fe 3+ of 4 eV. The width of the L -edge XES of Fe 3+ also depends strongly on the substitution sites (Mg or Si), meaning that its coordination environments might also be distinguishable based on the Fe L -edge XES spectra. These strong sensitivities to the Fe’s states suggest that the high-resolution Fe L -edge XES would be a useful experimental technique to investigate Fe-bearing silicate minerals.

Description: The problem of resolving the two aluminum sites in the 27 Al NMR spectrum of kaolinite has been unsuccessfully addressed for 30 years. A few years ago, it was shown that the two sites cannot be spectrally separated even by the use of high magnetic fields. Nevertheless, it is still possible to determine the NMR parameters of both sites. In this article, we present an alternative approach. We show that, at low magnetic field (7 T), the individual spinning sideband lineshapes of the outer satellite transitions are sensitive enough to differentiate information coming from the two aluminum sites. Thus, the isotropic chemical shift , the quadrupolar constant C Q , and asymmetry parameter Q of each site can be obtained by accurately fitting the full 27 Al MAS spectrum acquired at low magnetic field. In return, this approach requires a carefully acquired and post-treated 27 Al spectrum. It is concluded that the two sets of parameters ( = 7.5 ppm, C Q = 3.4 MHz, Q = 0.8) and ( = 8.0 ppm, C Q = 3.0 MHz, Q = 0.9) represent the best and the unique solution overall. Moreover, the accuracy of these experimental values is independently and fully supported by first-principles calculations of the electric field gradient. The approach presented in this article can be easily applied, not only to clays or aluminosilicate materials, but to any compounds where the NMR parameters of overlapping spectral lines have to be determined. This can also be extended to sites of unequal multiplicity and to other nuclei. Moreover, this methodology can be useful in the characterization of small structural changes occurring partly at one particular site. Indeed, when the NMR parameters are barely modified, the spectral signatures due to both affected and unaffected sites may strongly overlap, making the spectral resonances broad and badly resolved. In such a case, determining the isotropic chemical shift and the quadrupolar coupling parameters may help to exceed the simple qualitative analysis of structural changes by offering the possibility of discriminating between structural models via the experimental data.

Description: High-pressure synchrotron Mössbauer (SMS) and X-ray emission (XES) spectroscopic measurements were conducted to investigate the spin and valence states of iron in (Al,Fe)-bearing magnesium silicate glass (Mg 0.79 Fe 0.10 Al 0.10 Si 0.96 O 3 ) up to 126 GPa and 300 K. By analyzing the Fe K β emission spectra using the integrated relative difference (IRD) method, which accounts for the spectral broadening effects, the derived total spin momentum ( S ) of the iron in the glass shows no observable changes with pressure within the experimental uncertainties. A two-doublet fitting model representing two diverse local iron atomic environments was used to satisfactorily simulate the high-pressure SMS spectra of iron in the glass. The doublet with an averaged quadrupole splitting (QS) value of 1.94(±0.25) mm/s and chemical shift (CS) of 1.02(±0.25) mm/s at ambient conditions was assigned to be high-spin Fe 2+ , whereas the second doublet with QS = 0.83(±0.25) mm/s and CS = 0.49(±0.25) mm/s was assigned to be high-spin Fe 3+ . Increasing pressure continuously elevates the QS of Fe 2+ from ~2 mm/s at ambient pressure to 3.5 mm/s at 126 GPa, while Fe 3+ only exhibits a slight increase in the QS to 1.34(±0.25) mm/s. Comparing with previous experimental and theoretical studies on the local geometries and hyperfine parameters of silicate glasses and minerals, we conclude that the occurrence of the extremely high QS of Fe 2+ in our glass above ~40–50 GPa can be associated with the enhanced density and diverse distortions and geometries of the local Fe 2+ environments. Our combined XES and SMS results show that both Fe 2+ and Fe 3+ ions in Al-bearing silicate remain in the high-spin state, rather than undergoing a spin-pairing transition as proposed previously. Assuming that the silicate glass results can be used as an analog for understanding silicate melts, our results here indicate that iron ions likely experience significant changes in the local environments yet remain overall in the high-spin state in silicate melts at the extreme pressure and temperature conditions of the deep mantle.

Description: Chalcopyrite (CuFeS 2 ) and bornite (Cu 5 FeS 4 ) are the most abundant Cu-bearing minerals in hydrothermal Cu deposits, forming under a wide range of conditions from moderate-temperature sedimentary exhalative deposits to high-temperature porphyry Cu and skarn deposits. We report the hydrothermal synthesis of both chalcopyrite and bornite at 200–300 °C under hydrothermal conditions. Both minerals formed via the sulfidation of hematite in solutions containing Cu(I) (as a chloride complex) and hydrosulfide, at pH near the pK a of H 2 S(aq) over the whole temperature range. Polycrystalline chalcopyrite formed first, followed by bornite. Assuming that Fe behaves conservatively, the transformation of hematite to chalcopyrite involves a large increase in volume (~290%). The reaction proceeds both via direct replacement of the existing hematite and via overgrowth around the grain. Chemical exchanges between bulk solution and hematite are enabled by a network of micrometer-size pores. However, in some cases the chalcopyrite overgrowth develops large grain sizes with few apparent pores and in these cases fluid transport may have been via a network of fractures. Similarly to the replacement of hematite by chalcopyrite, bornite forms via the replacement of chalcopyrite. The reaction has a large positive volume (~230%), and proceeds both via chalcopyrite replacement and via overgrowth. This study shows that replacement reactions can proceed via coupled dissolution-reprecipitation even where there is a large volume increase between parent and product mineral. This study also provides further evidence about the controls of reaction pathways onto the final mineral assemblage. In this case, the host initial fluid was undersaturated with respect to Fe-bearing minerals. Upon slow release of Fe at the surface of hematite, a mineral assemblage of chalcocite, bornite, and finally chalcopyrite is expected. However, in practice chalcocite did not nucleate on the surface of hematite. Rather relatively slow nucleation of bornite enabled high concentrations of Fe to build up near the dissolving hematite, so that chalcopyrite (high-sulfidation experiments) or chalcopyrite+pyrite (low sulfidation) crystallized first.

Description: Beryl and euclase crystals from the Mina do Santino and the Jacú pegmatites in the Borborema Pegmatite Province in northeastern Brazil contain several generations of melt and fluid inclusions, which allow interpretation of P-T - X conditions responsible for beryl crystallization and for alteration of a primary pegmatitic mineral assemblage to a mixture of hydrothermal minerals (euclase, bertrandite, kaolinite, and quartz). Primary melt and fluid inclusions hosted by beryl were trapped simultaneously. However, their homogenization temperatures are significantly higher (870–900 °C) than the values previously reported for pegmatitic systems (〈712 °C) and should be treated with caution. An isobaric drop of temperature resulted in the exsolution of a fluid. A low-salinity CO 2 -enriched phase and a saline water-rich phase were trapped in pseudosecondary inclusions in beryl at a pressure of 2.1–2.7 kbar and temperature of 390–480 °C. Cooling of the country rocks below 400 °C caused a ductile-to-brittle transition and allowed infiltration of cold groundwater, which further decreased the temperature in the system to 190–240 °C. At the same time, the pressure dropped from a lithostatic (2.1–2.7 kbar) to a hydrostatic value (0.57–0.73 kbar). Consequently, minerals deposited under magmatic conditions (feldspars and beryl) became unstable and a newly formed hydrothermal mineral paragenesis (euclase, bertrandite, kaolinite, and quartz) overprinted the earlier one. The hydrothermal fluids responsible for the alteration differ from the earlier-exsolved fluids in having a lower salinity, lower homogenization temperature, the absence of CO 2 , and the presence of CH 4 .

Description: Raman spectra of quartz inclusions in garnet hosts of low-pressure/temperature metamorphic rocks from the Yanai district in the Ryoke belt (around 0.1–0.3 GPa/500–600 °C), Southwest Japan, exhibit frequency (peak position) shifts toward lower wavenumbers as compared to those of a quartz standard measured at ambient conditions. The observed negative frequency shifts indicate that tensile normal stress is exerted on the quartz–garnet boundary and therefore, quartz inclusions are subjected to negative residual pressure. Elastic modeling that assumed the constant elastic properties of minerals cannot explain this negative residual pressure. This study estimated the residual pressure based on a new scheme of elastic modeling with equation of state (EOS) of quartz and garnet, which takes into account the pressure- and temperature-dependency of compressibility and expansivity. The calculated residual pressure was converted into frequency shifts of quartz Raman spectrum based on the experimentally determined relation. The results showed that the quartz inclusions in garnets retain residual pressure of about –0.3 GPa, and logically reproduced the observed frequency shifts in the direction of lower wavenumbers. The new elastic modeling also simulates positive frequency shifts retained by quartz inclusions in garnets of high-pressure metamorphic rocks from the Sambagawa metamorphic belt in Southwest Japan, and from the Motagua fault zone in Guatemala. The degree and direction of Raman frequency shifts of quartz inclusion in garnet depend on metamorphic conditions when the quartz was included in the host garnet. Conversely, the metamorphic conditions prevailing when a set of a quartz inclusion and garnet host was recrystallized can be inferred from Raman frequency shifts of quartz inclusion in garnet. The proposed Raman spectroscopic analysis should be a powerful and useful tool to decipher information at earlier stage of garnet growth even in samples of highly recrystallized matrix phases during exhumation and retrograde stages.

Description: The crystal chemistry of nine Cr-spinels from lherzolite and harzburgite xenoliths from the Middle Atlas Neogene-Quaternary Volcanic Field of Morocco have been studied by means of X-ray single-crystal diffraction and electron microprobe analyses. Cell edges are usually within the range 8.13–8.14 Å, but there are three samples with longer a value, so that the whole analyzed series is within the range 8.1334(4)–8.2021(2) Å, while the oxygen positional parameter values are very similar ranging between 0.2626(1) and 0.2629(2) for all of them. The cation distribution shows that the crystal structure is ordered with almost all divalent cations in the tetrahedral site and trivalent cations in the octahedral site. The determined intracrystalline temperatures are in the range 550–750 °C that are the lowest values ever found for Cr-spinels from mantle xenoliths as these are usually higher than 730 °C. If we consider the behavior of some geotherms from literature, the determined temperatures are confined in a depth range of about 20–40 km. Lithospheric models for the studied area indicate that the lower crust reaches its deepest value in a range between 30 and 40 km. Consequently, we can assume that the studied xenoliths were emplaced at a "shallow" depth of about 20–30 km, just beneath the lower crust, where they were disrupted and brought to the surface from the ascending alkaline lavas. This assumption is consistent with the concomitant presence of some crustal xenoliths. It is important to notice that even in the case of a mantle xenoliths where all the silicates could be heavily altered, the presence of one single crystal of Cr-spinel and the study of its oxygen coordinates ( u ), inversion parameters ( i ), Cr content, and calculated closure temperatures can be used to validate the thermal history of the mantle xenoliths. The combined approach of structural data, intra- and inter-crystalline temperatures, and the literature geophysical data seems to be an interesting tool to assess the pre-exhumation history of the mantle xenoliths.

Description: In a recent of issue American Mineralogist , Rollin-Martinet et al. (2013 , vol. 98, p. 2037–2045) take a thermodynamic, in contrast to a medical-biological, approach to the maturation process of biological apatite. They do so by focusing on changes in the HPO 4 2– concentration in biomimetic apatite over time. In this first-of-its-kind analysis, they conclude that the increase in stability of bone mineral over time ultimately demands that bone be remodeled (i.e., replaced by new bone) in order for the mineral to retain its biologically important functional properties.

Description: New data based on a detailed analysis of pyroxene zoning strongly suggests that convection is an important process in lunar magmas. Elardo and Shearer (2014) carefully document irregular oscillatory zoning that is best explained by movement of pyroxene crystals in a convecting magma. Lunar samples that contain such data are rare, but this study should inspire more extensive efforts to further document magmatic processes.

Description: Combining new measurements of thermal diffusivity ( D ) and viscosity () of 13 silica-rich glasses and their melts with previous data reveals specific effects of Al, Ca, and Fe cations on heat and mass transport for diverse glasses and melts. We investigated rhyolites, tektites, leucogranite, haplogranite, and chemically complex commercial glasses. Highly polymerized samples, with high-Al but low-Ca contents, yield high values for , D , and glass transition temperatures ( T g,12 ), whereas less polymerized samples with high-Ca but low-Al contents, have low , D , and T g,12 . Upon crossing the glass transition, D decreases substantially, to ~0.35 mm 2 /s for Ca-rich melts, but D decreases only weakly, to ~0.52 mm 2 /s for Al-rich melts. The magnitude of the decrease in D at T g,12 correlates with the melt fragility, and also to the configurational heat capacity. High-Ca contents result in low D for glasses and melts, whether or not Al is present. At high T , D / T is positive for glasses and melts containing Fe 2+ , which we attribute to diffusive radiative transfer involving electronic-vibronic coupling. Thermal conductivity of all glasses increases with T , flattening out as the transition is approached. For melts with 〉1 wt% FeO total , k / T is positive. We predict that upon melting, I-type arc granite liquids should have lower thermal diffusivity than calcium-poor A- or S-types, and calc-alkaline basalts will have lower D than tholeiitic basalts, such that D of granitic melts is ~0.2 mm 2 s –2 higher than basaltic. Ferrous iron enhancing heat transport could alter the predicted order at higher temperatures.

Description: Césarferreiraite, Fe 2+ Fe 2 3+ (AsO 4 ) 2 (OH) 2 ·8H 2 O, is a new laueite-group mineral (IMA 2012-099) of triclinic symmetry, from Eduardo pegmatite mine, Conselheiro Pena municipality, Minas Gerais, Brazil. Intimately associated minerals are pharmacosiderite, scorodite, and earlier arsenopyrite, and probably césarferreiraite replaces the latter. It occurs as fibrous-to-tabular aggregates up to 2 mm. Single crystals, up to 10 μm long with a thickness of about 1–2 μm, are elongated along [001] and flattened on (100). The fibers have almost rectangular cross-section apparently bound by the {100} and {010} pinacoid forms. Color and streak are pale to greenish yellow. Luster is vitreous; individual crystals are transparent and masses are translucent. Cleavage is distinct, presumably on {010} and {100}. Calculated density is 2.934 g/cm 3 . The mineral is biaxial (+), n (min) = 1.747(3), n (max) = 1.754(3) (589 nm). IR spectrum of césarferreiraite is unique and can be used for the identification of the mineral. Chemical composition ( n = 4, WDS, calculated for the condition Fe 2+ :Fe 3+ = 1:2, H 2 O for the ideal structural formula, wt%) is: FeO 11.50, Fe 2 O 3 25.56, CaO 15.41, As 2 O 5 33.51, H 2 O 26.01, total 100.12. The empirical formula (based on 18 O apfu) is Fe 2+ 0.98 Fe 3+ 1.96 [(AsO 4 ) 1.79 (PO 4 ) 0.31 ](OH) 1.52 ·8.08H 2 O. The strongest eight X-ray powder-diffraction lines [ d in Å( I )( hkl )] are: 9.85(95)(010), 6.35(100)(001), 3.671(29)(21), 3.158(32)(10), 2.960(39)(02), 2.884(35)(31), 2.680(29)(11), and 2.540(23)(10). Unit-cell parameters refined from powder data indexed by analogy with related laueite-group minerals (space group: P ) are: a = 5.383(2), b = 10.363(3), c = 6.878(2) Å, α = 96.42(4), β = 109.19(3), = 102.30(2)°, V = 347.1(2) Å 3 , and Z = 1. Gladstone-Dale compatibility is –0.020 (excellent). Césarferreiraite is the arsenate analog of ferrolaueite.

Description: Meteorite Northwest Africa (NWA) 6963 was classified as a basaltic shergottite based on mineralogy, but here we show that it is a gabbroic rock with a quartz-alkali feldspar intergrowth that represents a late-stage granitic melt. NWA 6963 contains clinopyroxene and maskelynite grains up to 5 mm in length, with minor ferroan olivine, spinel, ilmenite, merrillite, apatite, Fe-sulfides, and high-Si glass. NWA 6963 also contains areas of quartz and alkali-feldspar intergrowths up to ~1 mm in size. Based on mineral abundances and textural analysis, we suggest that NWA 6963 is an intrusive rock similar to a terrestrial gabbro. Infiltration of the martian crust by young gabbroic bodies would suggest that estimates of crustal composition, density, and thickness based on the surface chemistry alone would be problematic and the martian crust may be even more heterogenous than is seen from orbit alone. Investigations of crater walls, where intrusive crustal rocks would be exposed, are needed to discover the launch sites of the shergottites and the full heterogeneity of the martian crust.

Description: Speciation of D-O-H-C-N volatiles in alkali aluminosilicate melts and of silicate in D-O-H-C-N fluid has been determined in situ to 800 °C and 〉2 GPa under reducing and oxidizing conditions by using an externally heated hydrothermal diamond-anvil cell with Raman spectroscopy as the structural probe. Reducing conditions were near those of the IW oxygen buffer, whereas oxidizing conditions were obtained by conducting the experiments with oxidized components only and with Pt as a catalyst. Raman bands assigned to C-H stretching in CH x D y isotopologues and CH 4 groups (including CH 3 ) were employed to determine the CH 4 /CH x D y ratio in fluids and melts. This ratio decreases from 1.5–2 at 500 °C to between 1.2 and 1 with 800 °C with H -values of 13.6 ± 2.1 and 5.5 ± 1.1 kJ/mol for melt and fluid, respectively. The CH 4 /CH x D y fluid/melt partition coefficient ranges between ~16 and ~3 with H = 33 ± 6 kJ/mol assuming no pressure effect. This behavior of deuterated and protonated complexes is ascribed to speciation of volatile and silicate components in fluids and melts in a manner that is conceptually similar to D/H partitioning among complexes and phases in brines and hydrous silicate systems. Molecular N 2 is the N-bearing species in fluids and melts under oxidizing conditions. Under reducing conditions, the dominant species are molecular NH 3 and ammine groups, NH 2 – . The NH 3 /NH 2 ratio varies between 0.15 and 0.75 in the 425–800 °C temperature range. The enthalpy change of the ammonia/ammine equilibrium, H , derived from the temperature and assuming no pressure effect on the equilibrium, is 19 ± 8 and 61 ± 9 kJ/mol for melt and fluid, respectively. The fluid/melt partition coefficient, (NH 3 + NH 2 – ) fluid /(NH 3 + NH 2 – ) melt , ranges from 8 to 3 with H = 45 ± 12 kJ/mol. For oxidized nitrogen, the fluid/melt partition coefficient is twice or more of those values for reduced nitrogen. Hydrogen bonding can be detected at 500 °C and below. This behavior resembles that of H 2 O. Deuterium-containing analogues of the (N+H)-species could not be detected with precision because these were in the frequency-range of the second-order Raman shift of diamond in the diamond-anvil cell itself and could not be isolated from the strong background generated by the Raman intensity from the diamond. These results imply that, unlike noble gases, degassing of N-bearing species from the mantle is redox dependent, and is also more efficient at lower temperatures (shallow depths). Reduced and oxidized C-O-H-N species exist fluids and melts in the modern mantle, whereas reduced species dominated in the young Earth. The f H 2 -dependent speciation C-O-H-N volatile components result in f H 2 -dependent thermodynamic and transport properties of fluids and melts in the interior of the Earth and terrestrial planets. In fluids, the solubility of nominally incompatible trace elements can increase by orders of magnitude upon its saturation with silicate components. Trace element and stable isotope partitioning between fluids and melt can change by 〉100% for the same reason.

Description: The accumulation of metals and metalloids in diagenetic pyrite framboids is of interest because framboids can be a sink for heavy metal contaminants, a source of metals in ore deposits, and a tool to interpret paleo-ocean chemistry. In this study, we have used laser ablation-inductively coupled plasma-mass spectrometry (LA-ICPMS) to analyze pyrite framboids from both the contaminated Derwent Estuary and the uncontaminated Huon Estuary in Tasmania, Australia. While the enrichment of many trace metals in the Huon Estuary followed expected trends, the trends in the Derwent were quite different. In addition to the expected high contents of Pb, Zn, and Cu in the contaminated interval it was found that several elements are not as strongly incorporated into pyrite within the contaminated zone. It is suggested that this is due to over-competition for adsorption sites on the growing iron sulfides in the contaminated zone resulting in diffusion of several elements to deeper levels in the sediments. This results in an increase of these elements in pyrite below the zone of major contamination. The LA-ICPMS technique also provided the opportunity to obtain accurate data on gold, silver, and tellurium in pyrite, something rarely achieved in sequential leach extractions due to the low concentrations of these metals observed in nature.

Description: Mathesiusite, K 5 (UO 2 ) 4 (SO 4 ) 4 (VO 5 )(H 2 O) 4 , a new uranyl vanadate-sulfate mineral from Jáchymov, Western Bohemia, Czech Republic, occurs on fractures of gangue associated with adolfpateraite, schoepite, čejkaite, zippeite, gypsum, and a new unnamed K-UO 2 -SO 4 mineral. It is a secondary mineral formed during post-mining processes. Mathesiusite is tetragonal, space group P 4/ n , with the unit-cell dimensions a = 14.9704(10), c = 6.8170(5) Å, V = 1527.78(18) Å 3 , and Z = 2. Acicular aggregates of mathesiusite consist of prismatic crystals up to ~200 μm long and several micrometers thick. It is yellowish green with a greenish white streak and vitreous luster. The Mohs hardness is ~2. Mathesiusite is brittle with an uneven fracture and perfect cleavage on {110} and weaker on {001}. The calculated density based on the empirical formula is 4.02 g/cm 3 . Mathesiusite is colorless in fragments, uniaxial (–), with = 1.634(3) and = 1.597(3). Electron microprobe analyses (average of 7) provided: K 2 O 12.42, SO 3 18.04, V 2 O 5 4.30, UO 3 61.46, H 2 O 3.90 (structure), total 100.12 (all in wt%). The empirical formula (based on 33 O atoms pfu) is: K 4.87 (U 0.99 O 2 ) 4 (S 1.04 O 4 ) 4 (V 0.87 O 5 )(H 2 O) 4 . The eight strongest powder X-ray diffraction lines are [ d obs in Å ( hkl ) I rel ]: 10.64 (110) 76, 7.486 (200) 9, 6.856 (001) 100, 6.237 (101) 85, 4.742 (310) 37, 3.749 (400) 27, 3.296 (401) 9, and 2.9409 (510) 17. The crystal structure of mathesiusite was solved from single-crystal X-ray diffraction data and refined to R 1 = 0.0520 for 795 reflections with I 〉 3( I ). It contains topologically unique heteropolyhedral sheets based on [(UO 2 ) 4 (SO 4 ) 4 (VO 5 )] 5– clusters. These clusters arise from linkages between corner-sharing quartets of uranyl pentagonal bipyramids, which define a square-shaped void at the center that is occupied by V 5+ cations. Each pair of uranyl pentagonal bipyramids shares two vertices of SO 4 tetrahedra. Each SO 4 shares a third vertex with another cluster to form the sheets. The K + cations are located between the sheets, together with a single H 2 O group. The corrugated sheets are stacked perpendicular to c. These heteropolyhedral sheets are similar to those in the structures of synthetic uranyl chromates. Raman spectral data are presented confirming the presence of UO 2 2+ , SO 4 , and molecular H 2 O.

Description: During a nanomineralogy investigation of the Allende meteorite with analytical scanning electron microscopy, two new minerals were discovered; both occur as micro- to nano-crystals in an ultrarefractory inclusion, ACM-1. They are allendeite, Sc 4 Zr 3 O 12 , a new Sc- and Zr-rich oxide; and hexamolybdenum (Mo,Ru,Fe,Ir,Os), a Mo-dominant alloy. Allendeite is trigonal, R , a = 9.396, c = 8.720, V = 666.7 Å 3 , and Z = 3, with a calculated density of 4.84 g/cm 3 via the previously described structure and our observed chemistry. Hexamolybdenum is hexagonal, P 6 3 / mmc , a = 2.7506, c = 4.4318 Å, V = 29.04 Å 3 , and Z = 2, with a calculated density of 11.90 g/cm 3 via the known structure and our observed chemistry. Allendeite is named after the Allende meteorite. The name hexamolybdenum refers to the symmetry (primitive hexagonal) and composition (Mo-rich). The two minerals reflect conditions during early stages of the formation of the Solar System. Allendeite may have been an important ultrarefractory carrier phase linking Zr-,Sc-oxides to the more common Sc-,Zr-enriched pyroxenes in Ca-Al-rich inclusions. Hexamolybdenum is part of a continuum of high-temperature alloys in meteorites supplying a link between Os- and/or Ru-rich and Fe-rich meteoritic alloys. It may be a derivative of the former and a precursor of the latter.

Description: Knowledge and understanding about radionuclides retention processes on the materials composing the engineered barrier (clay mineral and metallic container waste) are required to ensure the safety and the long-term performance of radioactive waste disposal. Therefore, the present study focuses on the competitiveness of clay and the metallic container in the process of adsorption/desorption of the radionuclides simulators of Am 3+ and UO 2 2+ . For this purpose, a comparative study of the interaction of samarium (chosen as chemical analog for trivalent americium) and zirconyl (as simulator of uranyl and tetravalent actinides) with both FEBEX bentonite and metallic container, under subcritical conditions, was carried out. The results revealed that the AISI-316L steel container, chemical composition detailed in Table 1 , immobilized the high-radioactive waste (HRW), even during the corrosion process. The ZrO 2+ was irreversibly adsorbed on the minireactor surface. In the case of samarium SEM/EDX analysis revealed the formation of an insoluble phase of samarium silicate on the container surface. There was no evidence of samarium diffusion through the metallic container. Samarium remained adsorbed by the container also after desorption experiment with water. Therefore, steel canister is actively involved in the HRW immobilization.

Description: The effect of the substitution of Ca with Co, on the phase transition and on the extension of the miscibility gap, was studied to model the general mechanism of phase transitions and solid solutions in (Ca,M 2+ )M 2+ Si 2 O 6 pyroxenes. Eleven pyroxenes with composition Ca 1–x Co 1+x Si 2 O 6 , (0 ≤ x ≤ 1) were therefore synthesized by piston cylinder at P = 3 GPa, and T between 1100 and 1350 °C. The samples were characterized by SEM-EDS, XRD powder diffraction, and TEM. The results were compared with those of Ca-Fe and Ca-Mg pyroxenes. The phase diagram of Ca-Co pyroxenes is similar to that of Ca-Fe and Ca-Mg ones, with a wide asymmetric miscibility gap, and higher solubility in the Ca-rich side of the gap. The solubility on the Ca-rich side of the gap is related to the radius of the cation substituting. The cell parameters of the Ca-Co pyroxenes undergo a sudden change at the composition of about 0.4 Ca apfu, due to the C 2/ c – P 2 1 / c phase transition. The change in volume with composition follows an ideal trend, in the C 2/ c phase, dictated by the ionic size of the substituting cation. Deviation from the C 2/ c behavior are instead observed in the P 2 1 / c field and ascribed to volume strain. The same turnover was found in Ca-Mg, Ca-Fe, and Ca-Mn pyroxenes. The C 2/ c – P 2 1 / c transition occurs with decreasing the M2 average cation radius, down to a critical value between 0.85 and 0.88 Å, depending on the series. A stabilization of the C 2/ c phase related to crystal field in Ca-Fe and Ca-Co pyroxenes is suggested by the analysis of the volume strain in the P 2 1 / c field. A key finding is that a miscibility gap may develop either by lattice strain related to cation substitution, within a series where all end-members have the same structure, or for the combined effect of lattice strain and a phase transition, as is the case for pyroxenes.

Description: Infrared spectroscopy and X-ray diffraction are used to evaluate the OH and H 2 O environments in 10 Å phase ("TAP"), nominally Mg 3 Si 4 O 10 (OH) 2 ·H 2 O. Two partially deuterated samples of TAP synthesized under different conditions have very similar IR spectra, indicating that the phase has a reproducible structural state. IR spectra were also collected of samples of fully Ni-substituted and partially deuterated TAP, and of samples heated for 1–2 h at 500 °C to remove structural H 2 O/D 2 O and leave behind bands due to OH/OD of the 2:1 layer. A high-pressure study of the Ni-TAP sample confirmed that the behavior of its H 2 O and OH/OD bands was analogous to that observed in previous studies of Mg-TAP. Comparison of the IR spectra of unheated, heated, and compressed samples has allowed three different types of Mg-OH (Mg-OD) stretching bands to be identified, two of which are further split, indicating subtle complexities in the TAP structure. The third band is identical to the band in talc. Two interlayer H 2 O stretching bands have been identified. The presence of an absorption feature that is broader than these interlayer H 2 O bands suggests that there is a second type of more weakly bonded H 2 O. On heating to 500 °C, the main interlayer H 2 O bands are lost, the talc-like band is unchanged, and shifts in the other Mg-OH band frequencies indicate a change in environment following the loss of the interlayer H 2 O. At the same time the signature of a silanol group is possibly revealed from the coincidence of band positions in the Mg-TAP and Ni-TAP spectra. The recognition of three distinct Mg-OH (Ni-OH) environments in Mg-TAP (Ni-TAP) is consistent with the structural model of TAP proposed by Welch et al. (2006) and Phillips et al. (2007) , in which the transformation from talc to TAP involves a key change from hydrophobic to hydrophilic character that enables hydration of the interlayer. A final level of complexity is indicated by the identification of a 3 c trigonal superstructure from single-crystal XRD, implying a structure analogous to that of the 3 T phengite polytype, with interlayer H 2 O fulfilling the role of K. The formation of additional OH groups when talc transforms to 10 Å phase increases the amount of water contained in 10 Å phase and may also occur in closely related phyllosilicates in the Earth’s mantle, such as intergrowths of chlorite with 10 Å phase. Moreover, the reproducibility of the key features of the IR spectra for different samples implies that this water content is fixed.

Description: FeSi remains crystalline up to at least 2350 (±200) K at 23 GPa and 2770 (±200) K at 47 GPa in a laser-heated diamond-anvil cell, showing that addition of silicon does not cause a large amount of melting point depression; the melting temperature of pure iron ranges from 2300 (±100) K to 2700 (±150) K between 20 and 50 GPa. The transition between (B20) and B2 (CsCl-structured) crystalline phases occurs at 30 (±2) GPa at all temperatures from 1200 to 2400 K. The resulting 5% density increase may cause an increase in the miscibility of silicon in iron at P 〉 30 GPa, with potential implications for the cores of small rocky planets such as Mars and Mercury.

Description: The infrared spectra of hydroxyl in synthetic hydrous wadsleyite (β-Mg 2 SiO 4 ) and ringwoodite (-Mg 2 SiO 4 ) were measured at room temperature up to ~18.8 GPa for wadsleyite and up to ~21.5 GPa for ringwoodite. High-temperature spectra were measured in an externally heated diamond-anvil cell up to 650 °C at ~14.2 GPa for wadsleyite and up to 900 °C at ~18.4 GPa for ringwoodite. The synthetic samples reproduce nearly all the important OH bands previously observed at ambient conditions. Only subtle changes were observed in the infrared spectra of both minerals, both upon compression at room temperature and upon heating at high pressure. For wadsleyite, upon compression to ~18.8 GPa, the frequencies of the bands at ~3600 cm –1 remain almost unchanged, while the main bands at 3200–3400 cm –1 shift to lower frequencies. During heating at 14.2 GPa to 650 °C the bands at 3200–3400 cm –1 broaden and shift to slightly lower frequencies. For ringwoodite, upon compression to ~21.5 GPa, the main bands at 3115 cm –1 progressively shift to lower frequencies. During heating at 18.4 GPa to 900 °C, no frequency shift was observed for the band at ~3700 cm –1 , but the band initially at ~3115 cm –1 shifts very slightly to higher frequencies, which should yield almost the same band positions at 1300–1400 °C as those measured at ambient conditions. Our data suggest that water speciation in hydrous wadsleyite and ringwoodite at ambient conditions may be comparable to that under mantle conditions, except perhaps for subtle changes in hydrogen bonding. The low OH-stretching frequencies in wadsleyite and ringwoodite under transition zone conditions imply a large H/D fractionation during degassing of the deep mantle. This may explain the apparent disequilibrium between the hydrogen isotopic composition of the upper mantle and the ocean.

Description: The effect of pH on the kinetics of chrysotile dissolution was investigated at 25 °C in batch reactors over the pH range of 1 to 13.5, in oxalic solutions and buffered solutions of inorganic salts. Dissolution rates were obtained based on the release of Si and Mg. Results of the batch with inorganic buffers showed a strong dependence of dissolution rates on pH in the acid range. The logarithm of dissolution rates decreases with the pH with a slope of n = 0.27. Around neutral pH, a minimum is reached. From pH 8 to 12, rates increase again when pH increases, and follow a linear dependence with a shallow slope ( n = 0.06). The Mg/Si ratio shows a non-stoichiometric dissolution reaction with a preferential release of Mg 2+ at acidic pH; it decreases at neutral pH conditions according to Mg solubility. Our results suggest that the relative ease of the breaking of Mg-O bonds compared with Si-O bonds lead to dissolution via a series of steps involving Si and Mg, where Si release is the rate-limiting step. In the presence of 15 mmol L –1 oxalate, an intense catalytic effect from pH 1 to 6 is observed because of the capacity of the oxalate anion to form different complexes with Mg. The ratio of the rates derived from Mg and Si concentrations confirm an enhancement of non-stoichiometric dissolution compared with the series without oxalate. The mechanism of catalysis involves different processes depending on pH: At pH 1, XRD analysis confirms the formation of an amorphous silica phase dissolving all the Mg present in the chrysotile structure. At pH 2, XRD and FTIR results also confirm the precipitation of glushinskite, a magnesium oxalate phase. At pH 3 to 6, the presence of oxalate enhances dissolution almost by an order of magnitude compared with the experiments in inorganic buffered solutions. In this case, the mechanism could be due to the formation of aqueous or surface magnesium oxalate complexes. However, dissolution rates at neutral pH in the presence of oxalate are similar to those obtained in inorganic buffered solutions; the pH dependence at pH 8 to 13 is minimal. The increase in saturation and the drastic decrease in Mg solubility at these pH values could lead to precipitation of secondary phases coating the reactive mineral surface and inhibiting the surface. Results obtained in this study show that chrysotile dissolves faster in acid media and oxalate acts as a strong catalyst increasing the efficiency of magnesium release to solution at ambient temperature. These data may provide an excellent background to design and select optimal conditions in the previous acid treatment for carbon capture processes, as well as help to develop remediation process of asbestos contaminated sites.

Description: We studied the atomic structure and the chemical composition of (101)-type rutile (TiO 2 ) twins from Diamantina in Brazil by electron microscopy methods to resolve the mechanism of their formation. The twin boundaries were studied in two perpendicular orientations to reveal their 3D structure. The presence of a precursor phase, such as Al-rich hydroxylian pseudorutile (HPR; kleberite), during the initial stages of the crystallization appears to be the necessary condition for the formation of (101) twins of rutile at this locality. The precursor with a tivanite-type structure serves as a substrate for the topotaxial crystallization of rutile. Depending on the initial crystallization pattern the rutile can grow either as a single crystal or as a twin. During the progressive crystallization of the rutile Al-rich oxyhydroxide (diaspore, α-AlOOH) clusters are concentrated at the center of the precursor where they are pinned to the twin boundary as the precursor is fully recrystallized into rutile. At the increased temperatures the remaining diaspore precipitates are converted to corundum (α-Al 2 O 3 ), while the two crystal domains continue to grow in the (101) twin orientation. In addition to the primary (101) twin, series of secondary {101} twins are formed to accommodate the residual tensile stress caused by the diaspore-to-corundum transformation. Based on the observed corundum-rutile [0001] C (110) C ||[010] R (101) R and ilmenite-rutile [0001] I (100) I ||[010] R (301) R crystallographic relations a unified mechanism of the genesis of the {101} and {301} reticulated sagenite twin clusters is proposed.

Description: Knowledge of the thermodynamic mixing properties of amphiboles whose compositions lie along the tremolite-glaucophane join is of interest to those studying high-pressure metamorphic rocks as well as rocks transitional between the greenschist and blueschist facies. This study is the second of a two-part investigation of the tremolite-glaucophane join, with the first study ( Jenkins et al. 2013 ) devoted to the volume composition and crystal chemical relations, and the current study focused on defining the location and extent of asymmetry of the miscibility gap (solvus) along this join. A series of experiments was done over the temperature range of 500–800 °C at pressures of 1.6–1.9 GPa to determine the location of the miscibility gap using both two-amphibole dissolution experiments, including time-series experiments at 700, 750, and 800 °C lasting up to 670 h, as well as various end-member and intermediate amphibole overgrowth techniques to approach the boundary from different compositional directions. These results, which placed some important limits on the location of the miscibility gap, were combined with an autocorrelation analysis of the mid- and far-infrared spectra of single-phase amphiboles formed in the first study ( Jenkins et al. 2013 ) to refine the shape of the miscibility gap. Derived values of the relative change in the autocorrelation parameter ( Corr ) were fairly constant over all of the frequency ranges analyzed and indicated that the miscibility gap is steeper at the glaucophane-rich compared to tremolite-rich side of the binary join. Combining the compositional re-equilibration experiments with the infrared autocorrelation results permitted deriving the ratio of the parameters α Gl /α Tr = 0.5 and W TrGl = 67–70 kJ using asymmetric formalism theory. The calculated boundary has a critical-point temperature that falls in the range of 760–800 °C in this iron-free system. The asymmetry of the calculated miscibility gap appears to be confirmed by amphibole pairs in nature. The implications of this study are that this technique of combining compositional re-equilibration experiments with autocorrelation analysis of single-phase solid solutions is a potentially powerful method of locating miscibility gaps at low temperatures and for chemically complex binary joins. It is also suggested that the miscibility gaps presented here provide a basis for interpreting the degree of equilibrium reached in assemblages with complexly zoned or intergrown amphiboles.

Description: The mechanism of kaolinite transformation into dickite has been investigating using 13 samples from the Frøy and Rind oil fields (Broad Fourteens basin, North Sea), 3 kaolinite specimens with different crystal order (KGa-2, Kaolinite API 17, Keokuk kaolinite), and 2 dickite-rich samples (Natural History Museum collection). Detailed analysis of XRD, thermal analysis, and SEM data show that: (1) as dickite content increases, there is also an increase of the crystal order of kaolinite; (2) in dickite-rich specimens kaolinite and dickite have crystals (or XRD-coherent domains) of the same size; (3) there is no specific dehydroxylation temperature for each polytype, rather particle size and crystal order control dehydroxylation temperature independently of polytype; (4) with progressive dickite content, the development of both particle size and the size of the coherent crystal domains within particles is greater in the c direction than in the a - b plane; (5) the growth of defect-free segments in the c direction is not connected with the growth in the a and b directions, as would be expected in crystallization from solution; (6) textural features indicate coalescence of kaolin plates with burial; (7) there is a very weak positive correlation between particle dimensions and relative kaolinite-dickite content. These results are interpreted as resulting from a double reaction taking place in the solid state with burial. Some kaolinite domains grow in size and crystal order while other domains are transformed into dickite. Presumably, also the dickite domains formed early in the transformation grow in crystal order. The transformation into dickite stops at 90–95% dickite because the remaining kaolinite domains are so large and stable that the stability increase produced by the polytype transformation would be negligible.

Description: Thermophysical and thermochemical calorimetric investigations were carried out on synthetic analogs of two minerals: cobaltomenite (CoSeO 3 ·2H 2 O) and ahlfeldite (NiSeO 3 ·2H 2 O). The synthesis was realized by mixing of aqueous solutions of cobalt and nickel nitrates, accordingly, and sodium selenite, acidified with the help of a solution of nitric acid and characterized by X-ray powder diffraction and FTIR spectroscopy methods. The low-temperature heat capacities of CoSeO 3 ·2H 2 O and NiSeO 3 ·2H 2 O were measured using adiabatic calorimetry between 8 and 340 K, and the third-law entropies were determined. Values of S (298 K, CoSeO 3 ·2H 2 O, cr.) = 183.2 ± 1.0 J/(mol·K) and S (298 K, NiSeO 3 ·2H 2 O, cr.) = 172.9 ± 1.0 J/(mol·K) are obtained with an uncertainty of 0.5%. The enthalpies of formation for CoSeO 3 ·2H 2 O and NiSeO 3 ·2H 2 O were determined by solution calorimetry with H 2 SO 4 solution as the solvent and giving f H (298 K, CoSeO 3 ·2H 2 O, cr.) = –1135.3 kJ/mol, f H (298 K, NiSeO 3 ·2H 2 O, cr.) = –1133.3 kJ/mol. The Gibbs energy of formation for CoSeO 3 ·2H 2 O and NiSeO 3 ·2H 2 O at T = 298 K, 1 atm can be calculated on the basis on f H and f S : f G (298 K, CoSeO 3 ·2H 2 O, cr.) = –937.4 kJ/mol and f G (298 K, NiSeO 3 ·2H 2 O, cr.) = –932.4 kJ/mol. Smoothed C P ( T ) values between T = 0 K and T = 320 K for CoSeO 3 ·2H 2 O (cr.) and NiSeO 3 ·2H 2 O (cr.) are presented along with values for S and the functions [ H ( T )- H (0)] and [ G ( T )- H (0)]. These results motivate a re-evaluation of the natural conditions under which selenites, and selenates replace selenides, and sulfides in the oxidation zones of sulfide ore deposits or upon weathering of technologic waste. The values of f G for CoSeO 3 ·2H 2 O and NiSeO 3 ·2H 2 O were used to calculate the Eh-pH diagrams of the Co-Se-H 2 O and Ni-Se-H 2 O systems. These diagrams have been constructed for the average contents of these elements in acidic waters of the oxidation zones of sulfide deposits. The behavior of selenium, cobalt, and nickel in surface environments have been quantitatively explained by variations of the redox potential and the acidity–basicity of the mineral-forming medium. Precisely these parameters determine the migration ability of selenium compounds and its precipitation in the form of various solid phases.

Description: Carbonate-substituted hydroxylapatite is the inorganic component in bone. The nanometer size of bone crystallites and their interweaving with subequal volumes of collagen fibrils make the chemical analysis of the bone mineral extremely difficult. The few chemical analyses that are available commonly were made on ashed bone, which, in addition to mineral, also includes chemical residues of collagen. For the present study, we chose the rostrum of the whale Mesoplodon densirostris . Its mineral content of up to 96 wt% makes it an ideal material for pursuing the chemistry of bioapatite within bone. Both bulk (X-ray fluorescence, thermogravimetry, and carbon analysis) and point analyses and element mapping (electron microprobe) were applied to this densest of bone materials. Its bioapatite has an average carbonate content of ~8 wt% and an average Ca/P atomic ratio of 1.7. The rostrum shows extremely low-concentration trace elements (Al, Si, Fe, Ti, and Sr) and some minor elements (K and Cl) as in typical bone materials. Homogeneity of elemental distribution is demonstrated in typical mineral-dominated areas within the rostrum sections except around a few vascular holes and vessels. The very good correlation between electron microprobe point analyses and the XRF bulk analyses of the rostrum indicate the latter to be a useful chemical model of bone mineral. The bulk analysis shows that the bioapatite in the rostrum has an average composition of (Ca 8.40 Mg 0.20 Na 0.54 )[(PO 4 ) 4.87 (CO 3 ) 1.13 ](OH) 0.87 .

Description: High-pressure behavior of coesite was studied on single crystals using diamond-anvil cells with neon as the pressure-transmitting medium by means of in situ Raman spectroscopy up to pressures of ~51 GPa. The experimental observations were complemented with theoretical computations of the Raman spectra under similar pressure conditions. We find that coesite undergoes two phase transitions and does not become amorphous at least up to ~51 GPa. The first phase transition (coesite I to coesite II) is reversible and occurs around 23 GPa. The second transition (coesite II to coesite III) at about 35 GPa is also reversible but involves a large hysteresis. Samples recovered from the highest pressure achieved, ~51 GPa, show Raman spectra of the initial coesite. The ab initio calculations gave insight into the initiation mechanism of the first phase transition, implying, from the analysis of unstable phonon modes, that it is probably a displacive phase transition due to shearing of the four-membered rings of SiO 4 tetrahedra upon compression. The transition to the lowest-symmetry phase, coesite III, is possibly a first-order phase transition that leads to a very distinct structure. None of the metastable high-pressure phases of coesite has been previously studied and it was widely accepted that coesite undergoes pressure-induced amorphization at significantly lower pressures (30 GPa). The study of the high-pressure behavior of coesite is important to better constrain the metastable phase diagram of silica. Further crystallographic investigations are necessary for characterizing the structures of these metastable coesite forms. Crystalline or amorphous metastable phases derived from coesite under high-pressure conditions are of particular interest because they can be used as potential tracers of peak transient pressures (stress) reached in processes such as impacts or faulting.

Description: Qingsongite (IMA 2013-30) is the natural analog of cubic boron nitride (c-BN), which is widely used as an abrasive under the name "Borazon." The mineral is named for Qingsong Fang (1939–2010), who found the first diamond in the Luobusa chromitite. Qingsongite occurs in a rock fragment less than 1 mm across extracted from chromitite in deposit 31, Luobusa ophiolite, Yarlung Zangbu suture, southern Tibet at 29°13.86N and 92°11.41E. Five electron microprobe analyses gave B 48.54 ± 0.65 wt% (range 47.90–49.2 wt%); N 51.46 ± 0.65 wt% (range 52.10–50.8 wt%), corresponding to B 1.113 N 0.887 and B 1.087 N 0.913 , for maximum and minimum B contents, respectively (based on 2 atoms per formula unit); no other elements that could substitute for B or N were detected. Crystallographic data on qingsongite obtained using fast Fourier transforms gave cubic symmetry, a = 3.61 ± 0.045 Å. The density calculated for the mean composition B 1.100 N 0.900 is 3.46 g/cm 3 , i.e., qingsongite is nearly identical to synthetic c-BN. The synthetic analog has the sphalerite structure, space group F 3 m. Mohs hardness of the synthetic analog is between 9 and 10; its cleavage is {011}. Qingsongite forms isolated anhedral single crystals up to 1 μm in size in the marginal zone of the fragment; this zone consists of ~45 modal% coesite, ~15% kyanite, and ~40% amorphous material. Qingsongite is enclosed in kyanite, coesite, or in osbornite; other associated phases include native Fe; TiO 2 II, a high-pressure polymorph of rutile with the αPbO 2 structure; boron carbide of unknown stoichiometry; and amorphous carbon. Coesite forms prisms several tens of micrometers long, but is polycrystalline, and thus interpreted to be pseudomorphic after stishovite. Associated minerals constrain the estimated pressure to 10–15 GPa assuming temperature was about 1300 °C. Our proposed scenario for formation of qingsongite begins with a pelitic rock fragment that was subducted to mid-mantle depths where crustal B originally present in mica or clay combined with mantle N ( 15 N = –10.4 ± 3 in osbornite) and subsequently exhumed by entrainment in chromitite. The presence of qingsongite has implications for understanding the recycling of crustal material back to the Earth’s mantle since boron, an essential constituent of qingsongite, is potentially an ideal tracer of material from Earth’s surface.

Description: Despite the number of detailed studies on arsenate adsorption onto synthetic 2-line ferrihydrite carried out during the past few decades, questions remain regarding the fate of adsorbed arsenate during phase transformation of this poorly crystalline iron oxy-hydroxide. We assessed arsenate partitioning during this transformation by aging synthetic 2-line ferrihydrite with adsorbed arsenate (at an As/Fe molar ratio of ~0.017) for 7 days at 75 °C under highly alkaline conditions (pH ~10). X-ray diffraction patterns show that ~55% of the ferrihydrite converted almost entirely to hematite (with traces of goethite) after aging 7 days, accompanied by a ~54% loss of reactive surface area (BET). ICP-MS analyses indicate that despite this conversion and significant loss of surface area, the aqueous arsenate concentration decreased from ~1.48 to ~0.51 mg/L during the course of the experiment. XAS analyses suggest that the concentration of arsenate and its speciation are controlled by its incorporation into the hematite.

Description: Moganite, a newly approved mineral, is microcrystalline silica. Samples of microcrystalline silica varieties containing variable amounts of moganite have been analyzed using absorption infrared spectroscopy (IR). The main spectral differences between moganite and α-quartz occur in the wavenumber region below 650 cm –1 . Above this wavenumber, the frequencies of Si-O stretching vibrations of moganite are almost identical to those of quartz. Additional moganite bands were recorded near 165, 207, 296, 343, 419, 576, and 612 cm –1 , and several of these extra IR bands have been identified for the first time in moganite. The results indicate that moganite and quartz have different crystal structures and symmetries in terms of different tetrahedral linkages. Infrared spectra obtained from samples with different moganite contents cannot be simply explained by mechanical mixing of the two moganite and quartz end phases. The change in moganite content leads to not only a variation of spectral intensity, but also a systematic modification in band position and full-width at half maximum. This unusual behavior is attributed to grain size, strains, and stacking faults in moganite and the intergrowth of moganite with fine-grained quartz. The close correlation between band width and moganite content is indicative of an improved crystallinity with decreasing in moganite concentration that has been identified in natural quartz variations. The results imply that moganite may play a role in the formation or crystallization of microcrystalline quartz. The present IR application offers a new method to estimate the moganite content in microcrystalline silica varieties.

Description: The subsolidus and melting phase relations in the CaCO 3 -siderite system have been studied in multi-anvil experiments using graphite capsules at pressure of 6 GPa and temperatures of 900–1700 °C. At low temperatures, the presence of ankerite splits the system into two partial binaries: siderite + ankerite at 900 °C and ankerite + aragonite up to 1000 °C. Extrapolated solvus curves intersect near 50 mol% just below 900 °C. At 1100 and 1200 °C, the components appear to form single-phase solid solutions with space group symmetry R c , while CaCO 3 maintains aragonite structure up to 1600 °C and 6 GPa. The FeCO 3 solubility in aragonite does not exceed 1.0 and 3.5 mol% at 900–1000 and 1600 °C, respectively. An increase of FeCO 3 content above the solubility limit at T 〉 1000 °C, leads to composition-induced phase transition in CaCO 3 from aragonite, Pmcn , to calcite, R c , structure, i.e., the presence of FeCO 3 widens the calcite stability field down to the P-T conditions of sub-cratonic mantle. The siderite-CaCO 3 diagram resembles a minimum type of solid solutions. The melting loop for the FeCO 3 -CaCO 3 join extends from 1580 °C (FeCO 3 ) to 1670 °C (CaCO 3 ) through a liquidus minimum near 1280 ± 20 °C and 56 ± 3 mol% CaCO 3 . At X (Ca) = 0–30 mol%, 6 GPa and 1500–1700 °C, siderite melts and dissolves incongruently according to the reaction: siderite = liquid + fluid. The apparent temperature and X (Ca) range of siderite incongruent dissolution would be determined by the solubility of molecular CO 2 in (Fe,Ca)CO 3 melt. The compositions of carbonate crystals and melts from the experiments in the low-alkali carbonated eclogite ( Hammouda 2003 ; Yaxley and Brey 2004 ) and peridotite ( Dasgupta and Hirschmann 2007 ; Brey et al. 2008 ) systems are broadly consistent with the topology of the melting loop in the CaCO 3 -MgCO 3 -FeCO 3 system at 6 GPa pressure: a Ca-rich dolomite-ankerite melt coexists with Mg-Fe-calcite in eclogites at CaO/MgO 〉 1 and Mg-dolomite melt coexists with magnesite in peridotites at CaO/MgO 〈 1. However, in fact, the compositions of near solidus peridotite-derived melts and carbonates are more magnesian than predicted from the (Ca,Mg,Fe)CO 3 phase relations.

Description: This work was carried out within the framework of the European Space Agency and Japanese Aerospace Exploration Agency BepiColombo space mission to Mercury and intends to provide valid tools for the interpretation of spectra acquired by the MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS) on board of BepiColombo. Two C 2/ c augitic pyroxenes, with different Mg/Fe ratios and constant Ca contents, were investigated by in situ high-temperature thermal infrared spectroscopy and in situ high-temperature single-crystal X-ray diffraction up to temperatures of about 750 and 770 K, respectively. The emissivity spectra of the two samples show similar band center shifts of the main three bands toward lower wavenumbers with increasing temperature. In detail, with increasing temperature bands 1 and 2 of both samples show a much stronger shift with respect to band 3, which remains almost unchanged. Our results indicate that the center positions of bands 1 and 2 are strong functions of the temperature, whereas the center position of band 3 is a strong function of the Mg# [with Mg# = Mg/(Mg + Fe 2+ ) atomic ratio]. The analysis of the thermal behavior gives similar thermal expansion volume coefficients, α V , for the Mg-rich and Fe-rich samples, with α V = 2.72(8) and 2.72(7) x 10 –5 K –1 , respectively, using the Berman (1988) equation. This correspondence totally explains the band center shifts similarity between the two samples. Our data suggest that MERTIS spectra will be able to provide indications of C 2/ c augitic pyroxene Mg# and will allow a correct interpretation that is independent on the spectra acquisition temperature.

Description: The Lengenbach (Switzerland) Pb-As-Tl-Zn deposit was formed from a sulfide melt at about 500 °C during Alpine metamorphism, but details on its formation and especially the source of the metals are still under debate. In this study we present two sample sets to address these questions: MC-ICP-MS analyses of thallium isotopes in sulfides, sulfosalts, and melt inclusions from the Alpine metamorphic Lengenbach deposit in the Binn Valley of Switzerland, the non-metamorphic Wiesloch Mississippi Valley-type deposit in Southern Germany, and the Cu- and As-rich mineralization at Pizzo Cervandone about 2 km SW of the Lengenbach deposit, which has been discussed as potential source of the Lengenbach metals. LA-ICP-MS analyses of micas from the Lengenbach deposit and surrounding country rocks between the deposit and the Pizzo Cervandone to trace potential metal-bearing fluid pathways. We found that Tl isotope compositions expressed as 205 Tl values in all investigated samples range from –4.1 ± 0.5 to +1.9 ± 0.5. The whole variation can be seen in the Lengenbach deposit alone, which hence records considerable fractionation even during high-temperature processes involving a sulfide melt. This large range of 205 Tl is thought to be caused by nuclear volume-dependent fractionation. Interestingly, the common fahlores at Lengenbach behave differently from all other investigated sulfosalts: based on their heavy isotopic composition together with a low As/S-ratio, they do not seem to be crystallized from the sulfide melt, but are interpreted to have formed from hydrothermal fluids enriched in the heavy Tl isotopes. Although As mobilization in the gneisses and dolomites surrounding the Lengenbach deposit is evident based on secondary arsenites, no traces of such a country rock fluid could be found in fissure micas at Lengenbach. Hence, considerations involving K/Rb, Rb/Tl, As/S, and Pb/Tl ratios in the sulfides and micas imply that the element enrichment in the Lengenbach deposit is either pre-Alpine or related to peak metamorphism, but occurred definitely before mica growth at Lengenbach.

Description: Hutcheonite (IMA 2013-029), Ca 3 Ti 2 (SiAl 2 )O 12 , is a new garnet mineral that occurs with monticellite, grossular, and wadalite in secondary alteration areas along some cracks between primary melilite, spinel, and Ti,Al-diopside in a Type B1 Fractionation and Unidentified Nuclear effects (FUN) Ca-Al-rich inclusion (CAI) Egg-3 from the Allende CV (Vigarano type) carbonaceous chondrite. The mean chemical composition of type hutcheonite by electron probe microanalysis is (wt%) CaO 34.6, TiO 2 25.3, SiO 2 20.9, Al 2 O 3 15.7, MgO 2.1, FeO 0.7, V 2 O 3 0.5, total 99.8, giving rise to an empirical formula of Ca 2.99 (Ti 4+ 1.53 Mg 0.25 Al 0.17 Fe 2+ 0.05 V 3+ 0.03 )(Si 1.68 Al 1.32 )O 12 . The end-member formula is Ca 3 Ti 2 (SiAl 2 )O 12 . Hutcheonite has the Ia d garnet structure with a = 11.843 Å, V = 1661.06 Å 3 , and Z = 8, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.86 g/cm 3 . Hutcheonite is a new secondary phase in Allende, apparently formed by iron-alkali-halogen metasomatic alteration of the primary CAI phases like melilite, perovskite, and Ti,Al-diopside on the CV chondrite parent asteroid. Formation of the secondary Ti-rich minerals like hutcheonite during the metasomatic alteration of the Allende CAIs suggests some mobility of Ti during the alteration. The mineral name is in honor of Ian D. Hutcheon, a cosmochemist at Lawrence Livermore National Laboratory, California, U.S.A.

Description: The crystal chemistry of Cr-spinels included in spinel peridotite mantle xenoliths from Baker Rocks and Greene Point (northern Victoria Land, Antarctica) has been studied by single-crystal structure refinement and electron microprobe analysis. All crystals are characterized by a dominance of Al Cr substitution with minor evidences of Mg Fe 2+ substitution and pertain to the Mg-rich portion of the spinel sensu stricto-chromite join. The two groups of samples, Baker Rocks (BR) and Greene Point (GP), show distinct degree of cation order with the inversion parameter ranging from 0.17 to 0.20 for BR spinels and from 0.06 to 0.13 for GP crystals. Closure temperatures, computed by a geothermometer based on the M Al+ T Mg T Al+ M Mg intracrystalline exchange, range from 883 to 911 °C for BR spinels and from 592 to 675 °C for GP spinels. We show that this difference is due to the higher concentration in Fe 3+ in GP spinels that enabled a faster kinetics of the intracrystalline cation ordering reaction, allowing the GP spinels to reach a higher degree of cation ordering and then lower closure temperatures.

Description: Fluorowardite (IMA2012-016), NaAl 3 (PO 4 ) 2 (OH) 2 F 2 ·2H 2 O, the F analog of wardite, is a new mineral from the Silver Coin mine, Valmy, Iron Point district, Humboldt County, Nevada, U.S.A., where it occurs as a low-temperature secondary mineral in complex phosphate assemblages rich in Al, Na, and F. Fluorowardite forms colorless to white or cream-colored, tetragonal-pyramidal crystals up to 0.1 mm in diameter. The streak is white. Crystals are transparent to translucent, with vitreous to pearly luster. The Mohs hardness is about 5, the tenacity is brittle, the fracture is irregular, and crystals exhibit one perfect cleavage on {001}. The calculated density is 2.760 g/cm 3 . Optically, fluorowardite is uniaxial positive, with = 1.576(2) and = 1.584(2) (white light) and is non-pleochroic. Electron microprobe analyses (average of 8) provided: Na 2 O 6.27, CaO 1.74, MgO 0.42, Al 2 O 3 35.21, Fe 2 O 3 0.72, P 2 O 5 32.49, As 2 O 5 0.64, F 6.76, O=F –2.85, H 2 O 13.35 (structure), total 94.74 wt%. The presence of H 2 O and OH and the absence of CO 3 were confirmed by FTIR spectroscopy. The empirical formula (based on 14 anions) is: (Na 0.87 Ca 0.13 Mg 0.04 ) 1.04 (Al 2.96 Fe 3+ 0.04 ) 3.00 (P 1.96 As 0.03 ) 1.99 O 8.12 (OH) 2.35 F 1.53 ·2H 2 O. Fluorowardite is tetragonal, P 4 1 2 1 2, a = 7.077(2), c = 19.227(3) Å, V = 962.8(5) Å 3 , and Z = 4. The eight strongest lines in the X-ray powder diffraction pattern are [ d obs in Å( I )( hkl )]: 4.766(100)(004,103); 3.099(75)(211,203); 3.008(62)(115,212); 2.834(28)(204,213); 2.597(56)(205); 1.7628(32)(400,401); 1.6592(29)(multiple); and 1.5228(49)(423, 2·2·10). The structure of fluorowardite ( R 1 = 3.15% for 435 F o 〉 4 F ) contains layers parallel to {001} consisting of Al 6 ( = F, O, OH or H 2 O) octahedra, PO 4 tetrahedra, and NaO 6 (H 2 O) 2 polyhedra. The two independent Al 6 octahedra link by corner-sharing to form a square array. Each PO 4 tetrahedron shares corners with three adjacent octahedra in the same square array and a fourth corner with an octahedron in the next layer. The Na atoms reside in the "cavities" in the square array, forming bonds only to O atoms in the same layer. Of the two nearly identical OH sites in the wardite structure, only one is occupied by F in the fluorowardite structure. This is an interesting example of a structure in which OH and F are selectively incorporated into two different, but similar, sites as the result of rather subtle hydrogen bonding influences.

Description: Five spinel single-crystal samples within the ulvöspinel-qandilite series [(Fe 2– x Mg x )TiO 4 , 0.15 〈 x 〈 0.94] were synthesized and structurally and chemically characterized by X-ray diffraction and electron microprobe techniques. Site populations, derived from structural and chemical analysis, show that the tetrahedrally coordinated site (T) is exclusively populated by Mg 2+ and Fe 2+ , while the octahedrally coordinated site (M) is populated by Ti 4+ , Mg 2+ , Fe 2+ , and minor amounts of Fe 3+ . The inverse cation distribution is characterized by parallel substitution of Mg 2+ for Fe 2+ at both the T and M sites along the series. The variation in the unit-cell parameter from 8.527 to 8.495 Å is mainly related to the occurrence of Mg 2+ at the M site rather than the T site. In fact, the substitution of Mg 2+ for Fe 2+ yields significant variations in M-O (from 2.045 to 2.034 Å) and only limited variation in T-O (from 2.007 to 2.002 Å). In conjunction with data from the literature, the present study provide a basis for quantitative analyses of the variation in T Mg-O bond distance from 1.966 Å for Mg-poor ulvöspinel to 1.990 Å for the qandilite end-member.

Description: The crystal structure of Pb 21 [Si 7 O 22 ] 2 [Si 4 O 13 ] has been solved on crystals grown by crystallization from melt. The compound is hexagonal, P 6 3 / m , a = 9.9244(5), c = 34.2357(16) Å, V = 795.28(6) Å 3 , R 1 = 0.042 for 3361 unique observed reflections. The structure contains five symmetrically independent Si sites tetrahedrally coordinated by O atoms. The Si1O 4 , Si3O 4 , and Si4O 4 tetrahedra share corners to form branched heptameric [Si 7 O 22 ] 16– units, whereas the Si2O 4 and Si5O 4 tetrahedra form the tetrameric [Si 4 O 13 ] 10– anions. The structure contains six symmetrically independent Pb sites with the PbO n coordination polyhedra distorted due to the stereochemical activity of the lone electron pairs. The structure can be described as a stacking of layers of the two types, A and B. The A-type layer contains [Si 7 O 22 ] 16– units, Pb1, Pb2, Pb3, and Pb4 sites, whereas the B-type layer contains [Si 4 O 13 ] 10– anions, together with Pb5, Pb6, and Pb6A sites. Stacking of the layers can be described as a sequence ...AA'BAA'B..., where A and A' denote A layers with opposite orientations of the tripod-shaped silicate heptamers. The crystal structure of Pb 21 [Si 7 O 22 ] 2 [Si 4 O 13 ] has many similarities to that of hyttsjöite, which contains the same layers consisting of tripod-shaped [Si 7 O 22 ] 16– anions. In both title compound and hyttsjöite, the anions are stacked together in such a way that ellipsoidal cavities with dimensions of ca. 10 x 6 x 6 Å 3 are created. The cavities are occupied by the ClPb 6 octahedra in hyttsjöite and by "empty" Pb 6 octahedra in Pb 21 [Si 7 O 22 ] 2 [Si 4 O 13 ]. Analysis of structural and chemical complexity in the PbO-SiO 2 system indicates that the most chemically complex phases (in terms of complexity of relations between chemical components) appear to be the most complex from the structural point of view as well. The title phase is the most structurally and chemically complex phase in the system. Structural organization of crystalline phases in the PbO-SiO 2 system can be described as controlled by the Pb:Si ratio. For the phases with Pb:Si 〈2, their structures contain Pb 2+ ions and silicate anions. For the phases with Pb:Si 〈2, the structures contain "additional" O atoms, i.e., atoms that are not bonded to Si. These atoms form OPb 4 tetrahedra, which are the next strongest structural subunits in the structure after silicate anions. The structures of the phases with Pb:Si 〈2 can therefore be described as based upon silicate anions and polynuclear cationic units consisting of edge- and corner-sharing OPb 4 tetrahedra.

Description: Correianevesite, ideally Fe 2+ Mn 2 2+ (PO 4 ) 2 ·3H 2 O, is a new reddingite-group mineral approved by the CNMNC (IMA 2013-007). It occurs in a phosphate-rich granite pegmatite that outcrops near the Cigana mine, Conselheiro Pena, Rio Doce valley, Minas Gerais, Brazil. Associated minerals are: triphylite, lithiophilite, frondelite, rockbridgeite, eosphorite, vivianite, fairfieldite, leucophosphite, cyrilovite, phosphosiderite, etc. Correianevesite occurs as grayish-brown to reddish-brown transparent bipyramidal crystals up to 4 mm in size. The streak is white, and the luster is vitreous. Mohs hardness is 31/2. Cleavage is poor on (010). Fracture is laminated, uneven across cleavage. The measured density is 3.25(2) g/cm 3 ; the calculated density is 3.275 g/cm 3 . The mineral is biaxial (+), α = 1.661(5), β = 1.673(5), = 1.703(5), 2 V meas = 70(10)°, 2 V calc = 65.6°. The IR spectrum confirms the presence of H 2 O. The Mössbauer spectrum shows the presence of two sites for Fe 2+ and one site for Fe 3+ occupied in the ratio Fe1 2+ :Fe2 2+ :Fe 3+ = 39:55:6. The chemical composition is as follows (electron microprobe, H 2 O determined by gas chromatography of ignition products, Fe apportioned between FeO and Fe 2 O 3 based on Mössbauer data, wt%): MnO 29.21, FeO 21.74, Fe 2 O 3 1.54, P 2 O 5 34.59, H 2 O 12.6, total 99.68. The empirical formula, based on 11 O apfu, is H 5.78 Mn 1.70 Fe 2+ 1.25 Fe 3+ 0.08 P 2.015 O 11 . The strongest lines of the powder X-ray diffraction pattern [ d , Å ( I , %) ( hkl )] are: 5.08 (43) (020), 4.314 (28) (002, 210), 3.220 (100) (221, 202), 3.125 (25) (122), 2.756 (35) (103, 230), 2.686 (25) (222, 113), 2.436 (22) (123), and 2.233 (23) (411, 331). The crystal structure is solved ( R 1 = 0.0176). Correianevesite is orthorhombic, space group Pbna , a = 9.4887(2), b = 10.1149(2), c = 8.7062(2) Å, V = 835.60(3) Å 3 , Z = 4. The refined crystal-chemical formula is: (Fe 2+ 0.72 Mn 2+ 0.20 Fe 3+ 0.08 )(Mn 1.48 Fe 2+ 0.52 )(PO 4 ) 2 (H 2 O,OH) 3 .

Description: Minerals of the amphibole group are found in igneous rocks on Earth and other rocky bodies. Since the O(3) site of amphibole can contain OH, O 2– , F, and Cl, amphibole composition provides important information about water and halogen contents, oxidation state, and other features of its formation and alteration environments. However, the complexity of amphibole crystal chemistry means this information is difficult to extract. Furthermore, it has been regular practice in the era of the electron microprobe to neglect H and Fe 3+ analyses for amphibole, critically reducing the amount of information available in amphibole analyses in the literature. We have assembled models and insights from previous work to create a methodology that allows the estimation of magmatic H 2 O and Cl contents from existing amphibole analyses. Since the methodology requires use of a cation norm, we begin with a deeper investigation of the consequences of different cation normalization schemes for amphibole analyses, and provide grounds for deciding which scheme best fits a given amphibole analysis. We then show how the existing model of Popp and coworkers can be reversed to estimate the OH and [O(3)] O 2– contents of amphiboles in synthesis experiments. Using a synthetic data set collected from the literature (39 amphibole analyses), we calibrate a partitioning model for the OH/Cl competition on the O(3) site of igneous amphiboles \[ \begin{array}{l}{K}_{\hbox{ Cl }}={({X}_{\hbox{ Cl }}/{X}_{\hbox{ OH }})}_{\hbox{ amphibole }}/{([\hbox{ Cl }]/[\hbox{ OH }])}_{\hbox{ melt }}\\\relax \hbox{ ln\hspace{0.17em} }{K}_{\hbox{ Cl }}=6.59\hspace{0.17em}\hbox{ K }/(\hbox{ Na }+^{[\hbox{ A }]}\square )-0.679\hspace{0.17em}\hbox{ Mg }+0.487\hspace{0.17em}^{[6]}\hbox{ F }\hbox{ e }\end{array} \] where X signifies a mole fraction of an anion on the O(3) site; [Cl] and [OH] signify melt mole fractions of the anion in question on a one-oxygen (Stolper-Zhang) basis; K, Na, [A] , Mg, and [6] Fe signify the amount of each component in the amphibole in atoms per amphibole formula unit, with [A] denoting vacancies on the amphibole A site. We then combine the Popp et al. model with our new model to link the occupancy of the amphibole O(3) site and other crystal chemical parameters to the Cl and H 2 O content of melts crystallizing amphibole. The competition between OH and Cl for this site can be used to calculate the melt and amphibole OH/H 2 O contents, as well as the speciation of Fe in amphibole, provided that the Cl content of both the amphibole and its coexisting melt is known, without analyzing either phase for H or Fe 3+ /Fe 2+ . While the models in this paper should be recalibrated using future experimental data, this work shows that considerably more information about the volatile contents of magmas can be gleaned from amphibole than previously shown and provides additional information about the crystal chemistry of amphibole and how it affects Cl partitioning into minerals of this group.

Description: The temperature dependence of the unit-cell dimensions and the crystal structures of the fluorperovskite neighborite, NaMgF 3 (analyzed in the Pbnm setting of the space group), have been determined at 88 temperatures between 9 and 440 K from high-resolution, time-of-flight, powder neutron diffraction data. Lattice parameters exhibit saturation at low temperatures, before developing linear thermal expansion coefficients at temperatures above ~350 K. The temperature dependence of each axis has been analyzed, and fitted, using a two-term expression related to an Einstein internal energy function. The unit-cell parameters a and c behave in a conventional manner, however, an unexpected, and previously unobserved, region of negative linear thermal expansion has been found for the b axis in the temperature interval 20 ≤ T ≤ 90 K. Estimated, high-temperature axial thermal expansion coefficients derived from the lattice parameter fitting are in good agreement with those experimentally determined from an earlier synchrotron study, and indicate that high-temperature saturation has been achieved in neighborite by 440 K. The unit-cell volume varies smoothly and monotonically over the whole temperature interval, and the two-term Debye model of Barron has been successfully used to fit these data with characteristic temperatures of 369(2) and 1055(14) K. For the temperature interval 313.15–443.15 K, the thermodynamic Grüneisen constant has been determined using the Debye parameterization of the unit-cell volume, coupled with literature values of the isobaric molar heat capacity. The evolution of the crystal structure as a function of temperature is presented, and explained, in terms of the temperature dependence of the amplitudes of the seven symmetry-adapted basis-vectors of the aristotype phase that are consistent with the orthorhombic space group. The calculated temperature variations of the bond lengths are in excellent agreement with those experimentally determined. The primary order parameters for centrosymmetric, zone-boundary phase transitions in perovskite-structured compounds, i.e., the amplitudes of the basis vectors that transform as the irreducible representations R + 4 (anti-phase tilt) and M + 3 (in-phase tilt), have been fitted to a Landau free energy expansion that incorporates low-temperature saturation. Within the temperature range studied, the temperature dependence of the displacement corresponding to the anti-phase tilt is consistent with tricritical behavior. Experimental evidence is presented for a quadratic coupling of the in-phase tilt to the anti-phase tilt for temperatures greater than ~135 K, suggesting critical behavior at the orthorhombic–cubic transition is purely related to an instability at the R point of the pseudocubic Brillouin zone.

Description: The crystal structure and chemical composition of a crystal of (Mg 1– x Cr x )(Si 1– x Cr x )O 3 perovskite (with x = 0.07) synthesized in the model system Mg 3 Cr 2 Si 3 O 12 –Mg 4 Si 4 O 12 at 23 GPa and 1600 ºC have been investigated. The compound was found to be orthorhombic, space group Pbnm , with lattice parameters a = 4.8213(5), b = 4.9368(6), c = 6.9132(8) Å, V = 164.55(3) Å 3 . The structure was refined to R = 0.046 using 473 independent reflections. Chromium was found to substitute for both Mg at the dodecahedral X site (with a mean bond distance of 2.187 Å) and Si at the octahedral Y site (mean: 1.814 Å), according to the reaction Mg 2+ + Si 4+ = 2Cr 3+ . Such substitutions cause a shortening of the 〈X-O〉 and a lengthening of the 〈Y-O〉 distances with respect to the values typically observed for pure MgSiO 3 perovskite. Although high Cr-contents are not considered in the pyrolite model, Cr-bearing perovskite may be an important host for chromium in the lower mantle. The successful synthesis of perovskite with high-Cr content and its structural characterization are of key importance because the study of its thermodynamic constants combined with the data on phase relations in the lower-mantle systems can provide new constraints on thermobarometry of perovskite-bearing assemblages.

Description: Chevkinite-(Ce) and perrierite-(Ce) are the most common members of the chevkinite group of minerals. They are dimorphs, and both have the general formula A 4 BC 2 D 2 Si 4 O 22 , where A = REE, Y, Ca, Sr, Th; B = Fe 2+ , (Mn, Mg); C = Ti, Al, Fe 3+ , Fe 2+ , Cr, Mn, Mg, Zr, Hf, Nb; and D = Ti. Both have been reported from a wide range of igneous, metamorphic, and hydrothermal rocks types, but occurrences in mafic rocks are rare, with minimal chemical and crystallographic documentation. Chevkinite-(Ce) and/or perrierite-(Ce) occur with other Ti-, Zr-, and REE-bearing accessory phases in eight suites of tholeiitic dolerite from Western Australia, and in lunar mare basalt 10047. They are more abundant than has been recognized previously in mafic igneous rocks, and they are significant hosts of incompatible elements. Chevkinite-(Ce) and perrierite-(Ce) from mafic rocks have distinctive chemical compositions with higher Zr than recorded in examples from most other common rock types. Among mafic rocks, two groups are recognized based on total Fe contents in electron microprobe analyses: crystal structural analysis by electron diffraction indicates that the high-Fe group (〉8 wt% FeO) is chevkinite-(Ce), while the low-Fe group (〈8 wt% FeO) is consistent with perrierite-(Ce), and both minerals can occur within a single hand specimen. A previously proposed chemical discriminant is not applicable to chevkinite-group minerals from typical mafic igneous rocks and crystal structural information is required to unequivocally distinguish between the two dimorphs.

Description: The ubiquity of quartz in continental crust, and the involvement of SiO 2 in multiple metamorphic processes such as reactions, fluid flux, and solution-transfer processes, makes quartz an obvious choice for reconstructing prograde metamorphic conditions in various rock types. Recent studies have shown the usefulness of analyzing Ti distribution in quartz to constrain pressure-temperature-(relative) time-deformation ( P-T-t-D ) in metamorphosed tectonites. New high-precision single-crystal X-ray diffraction volume constraints on Ti-doped and chemically pure quartz provide further evidence for substitution of Ti 4+ for Si 4+ in the tetrahedral site in quartz, with resultant lattice strain on the structure. Recent applications of the Ti-in-quartz thermobarometer to dynamically recrystallized quartz have identified recrystallized subgrains that contain lower Ti concentrations ([Ti]) than their host porphyroclasts. In addition, [Ti] are lower than expected for the temperatures of recrystallization. Atomistic simulations that estimate energetic perturbations resulting from Ti incorporation into the quartz lattice indicate that significant increases in strain energy occur only at very high [Ti]; the strain-energy increase is negligible for [Ti] typical of quartz grown under mid-crustal conditions. This suggests that lattice strain rarely provides an appreciable driving force for Ti loss from quartz; instead, it appears that subgrain boundaries and dislocation arrays migrating through recrystallizing quartz crystals can promote localized re-equilibration, thermodynamically regulated by the composition of the intergranular medium (typically undersaturated in Ti). It therefore appears that analyses from dynamically recrystallized quartz cannot be meaningfully interpreted until methods are developed that can account quantitatively for the reduction of Ti resulting from crystal plastic flow.

Description: The present work reports the effects of irradiation on vermiculite for the first time. The radiation-induced changes of vermiculite were studied using different techniques viz. ultraviolet-visible spectroscopy (UV-Vis), dielectric measurements, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermoluminescence (TL). In UV-Vis analysis, the Cody model was employed to calculate structural disorder from Urbach energy, which explained the variation of the optical band gap (direct and indirect) with different (1–2000 kGy) doses. XRD analysis of the pristine and irradiated samples shows that the crystallinity improved upon irradiation at dose up to 1000 kGy and deteriorated on further increase of the dose. A significant change was observed in the dielectric properties after irradiation. Data shows that ac conductivity is proportional to the nth power of frequency ( f n ) in pristine and irradiated vermiculite, with a slope n ranging between 0.52 and 0.76, which indicates that electronic conduction takes place through an electron hopping process. No appreciable changes in characteristic bands (FTIR) have been observed after irradiation, indicating that natural vermiculite is chemically stable. A well-defined TL peak around 132 °C and enhancement in its intensity with dose (1–1000 kGy) make vermiculite a perfect thermoluminescence dosimeter and indicates usefulness applications in radiation dosimetry.

Description: Pyrochlore-supergroup minerals containing relatively high Si concentration are quite common in various geochemical parageneses, e.g., carbonatites, alkaline syenites, pegmatites. However, the role of Si and the mechanism of its incorporation into the structure of these minerals, although widely discussed, have not been explained definitively. Our paper reports the results of comprehensive SEM, EPMA, XRD, TEM, and MAS-NMR studies performed for the first time on a natural pyrochlore, which is the late-magmatic to early hydrothermal accessory component of the nepheline syenite in the alkaline Mariupol massif in Ukraine. It represents partly metamict, patchy-zoned, A -cation depleted, REE-, U-, and Th-bearing fluornatropyrochlore, locally exceptionally rich in SiO 2 (up to 13.01 wt%) that underwent both primary and secondary alterations, leading to kenopyrochlore or hydropyrochlore species. The primary alteration was induced by high-temperature, Ca 2+ - and Si 4+ -rich, and F – moderate fluids, which affected only some domains of the pyrochlore crystals and resulted in filling the A site vacancies mainly by Ca 2+ , but also Mn 2+ , Sr 2+ , and K + . The secondary alteration, induced by the exposure of the host rock to ground water driving fluid-mediated coupled dissolution-reprecipitation process, affected the whole pyrochlore crystals (both Si-enriched and Si-free domains) and caused, among others, the leaching of some A- and Y- site components. TEM investigations indicate that the selected-area electron diffraction patterns taken from Si-poor areas show strong and sharp diffraction spots related to well-crystalline pyrochlore, whereas the Si-rich areas show weaker spots with a diffuse diffraction halo that are typical of metamict material. Due to the fact that no intergrowth with other Si-bearing phases was observed in the TEM images even at very high magnification, it might be concluded that Si 4+ can occupy severely α-decay damaged and chemically altered portions of this structure. The absence of Si in the sixfold-coordinated B site has been corroborated both by compositional relationships, and by the lack of any [6] Si 4+ signal around –200 ppm in the MAS-NMR spectrum. A broad signal in the spectrum appearing at around –84 ppm, points to an amorphous species with tetrahedrally coordinated Si, close to Q (2) species defined as Si atom with two bridging O atoms, i.e., [Si(OSi) 2 (–) 2 ], in the form of finite-length chain-like structures, located in the damaged A and B sites of the primary structure.

Description: Garnet and other rock-forming minerals from A-type granite dikes in the Pre-Variscan Brno Batholith were analyzed to determine relative contributions of individual minerals to whole-rock Y and REE budget and to assess incorporation mechanisms of these elements in garnet. Minor to accessory garnet (〈2 vol%) is the essential reservoir for Y+REE in the Hlína granite accounting ~84% Y and 61% REE of the total whole-rock budget. Zircon is another important carrier of REE with ~13% Y and ~11% REE. At least ~21% REE and 1% Y were probably hosted by Th- and U-rich monazite that has been completely altered to a mixture of secondary REE-bearing phases. The contribution of major rock-forming minerals (quartz and feldspars) is low (~1% Y; 10% LREE; ~1% HREE) excluding Eu, which is hosted predominantly by feldspars (~90%). Minor to accessory muscovite and magnetite incorporate ~1% Y and ~2% REE of the whole-rock budget. Magmatic garnet Sps 41–46 Alm 28–44 And 0–13 Grs 6–12 Prp 0–1 is Y- and HREE-rich (up 1.54 wt% Y; up ~1 wt% REE), and the Y+REE enter the garnet structure via the menzerite-(Y) substitution. The Y and REE show complex zoning patterns and represent sensitive indicator of garnet evolution, in contrast to a homogeneous distribution of major divalent cations. General outward decrease of Y+REE is a common feature due to the strong partitioning of Y+HREE in the garnet relative to the other phases. REE underwent significant fractionation during growth of early garnet I; the Yb N /Nd N ratio generally decreases from the core to rim of garnet I. Higher Mn and Al, lower Ca, and Y+REE contents, as well as higher Yb N /Nd N ratio and more negative Eu anomaly in garnet II overgrowths indicate its crystallization from a more evolved melt. Application of zircon saturation geothermometry provides upper temperature limit of 734 ± 14 °C for the closed-system crystallization. Mineral equilibria reveal that crystallization started at QFM + 1.2, and preferential sequestration of Fe 3+ into garnet and magnetite was responsible for progressively reducing conditions. Equilibrium between magnetite, garnet, quartz, and plagioclase, representing the final crystallization stage of the granitic magma, occurred at 658–663 °C and QFM 0 to + 0.8, hence at undercooling of ~75 °C.

Description: Anorthositic rocks dominate the Moon’s upper crust. As remnants of the lunar magma ocean (LMO), small variations in the mineralogy of these rocks may hold key information about the homogeneity of LMO composition and solidification processes. Orbital near-infrared (NIR) sensors are sensitive to mineralogy, but technologic advances have only recently enabled detection of the plagioclase component in crustal rocks based on an absorption band centered near 1250 nm. Anorthosites occupy a unique mineralogic range that is well suited for NIR studies: the highly transparent component, plagioclase, is present in high abundances while the spectrally dominant mafic or oxide minerals are present in only minor abundance. As a result, spectra of anorthosites are more likely than many other rock types to contain visually discernable signatures from more than one mineral component, facilitating their identification and characterization in NIR data. In support of new NIR measurements for the Moon, we present laboratory spectral analyses of well-controlled plagioclase-dominated mineral mixtures. We focus on the spectral effects of varying mafic and oxide composition and abundance in mixtures with a common plagioclase end-member. The results demonstrate that plagioclase can be a significant contributor to reflectance spectra when strongly absorbing minerals are present in low abundance. We show that the contribution of plagioclase is more pronounced in mixtures with pyroxenes and certain spinels, but more easily masked in mixtures containing small amounts of olivine. Differences in minor mineral composition are clearly expressed in bulk spectra. Modeling of mixtures using a Hapke nonlinear approach accurately estimates mineral abundances in laboratory spectra to within 5 vol% for mixtures with ≥90 vol% plagioclase. Together, these results imply that not only should orbital NIR data sets be able to discern the presence of plagioclase in anorthositic crustal exposures, but also that detailed information about anorthosite mineral assemblages can be reliably accessed in reflectance spectra.

Description: Despite efforts to understand the amorphization mechanisms of zeolites upon heating and subsequent dehydration, little is known about the extent of Si-Al disorder and topological variations in both crystalline and amorphous phases during amorphization. In this study, we investigated the atomic structure and the extent of configurational disorder (e.g., Si-Al ordering) in Na-zeolite A and other dehydrated phases during their temperature-induced amorphization using multi-nuclear solid-state NMR. We also report the first multi-nuclear ( 17 O, 29 Si, and 27 Al) NMR spectra of the intermediate amorphous phases. 29 Si MAS NMR results confirm the prevalence of amorphous phases up to ~1073 K and variation in Q-species for the crystalline phases. The 27 Al quadrupolar coupling constant of the [4] Al peak in Na-zeolite A and the intermediate amorphous phases increase with increasing temperature, which suggests an increase in the topological disorder associated with the structural distortion around [4] Al. 2D 17 O 3QMAS NMR spectra resolve the crystallographically distinct Si-O-Al sites in Na-zeolite A and three types of oxygen linkages namely, Si-O-Al, Si-O-Si, and Al-O-Al in the intermediate amorphous phases, which provides an unambiguous experimental evidence for an increase in the Si-Al disorder during the amorphization of zeolite. The detailed structural changes in Na-zeolite A and other dehydrated phases at various temperatures provide insights into the structural changes of other aluminosilicates during amorphization, thereby highlighting the changes in Si-Al ordering.

Description: This paper explores the crystal chemical features of the bulk and the outermost (001) surface layers of two trioctahedral Li-rich mica-1 M (space group C 2) polytypes, i.e., a polylithionite (MLG-114) from Li-mica granitic pegmatite at St. Austell (SW England) and a Fe 2+ -rich polylithionite (Ch-140) from a rhyolite at Profitis Ilias, Chios Island, Greece. Structural formulas are [xii] (K 0.952 Na 0.019 Rb 0.019 ) [vi] (Al 1.034 Li 1.459 Fe 0. 2+ 389 Fe 0. 3+ 046 Mn 0.038 Mg 0.002 Zn 0.002 Ti 0.001 ) [iv] (Al 0. 3+ 477 Si 3.523 )O 10.081 (F 1.735 OH 0.184 ) and [xii] (K 0.992 Na 0.014 ) [vi] (Al 0.980 Li 1.028 Fe 0. 2+ 787 Fe 0. 3+ 022 Mn 0.059 Mg 0.052 Zn 0.010 Ti 0.024 ) [iv] (Al 0. 3+ 857 Si 3.143 ) O 10.095 (F 1.617 OH 0.288 ) for MLG-114 and Ch-140, respectively. Each mineral is characterized by a high F content in the anion site and has tetrahedral and octahedral compositions related to the exchange vector [vi] Li –1 [iv] Si –1 [vi] Fe 2+ [iv] Al. Unit-cell dimensions are a = 5.251(1), b = 9.066(2), c = 10.087(2) Å; β = 100.694(5)° for polylithionite MLG-114 and a = 5.282(1), b = 9.121(3), c = 10.080(3) Å; β = 100.764(5)° for Ch-140. Crystal structure refinements (agreement factors are R = 3.58% and 3.75% for MLG-114 and Ch-140, respectively) demonstrate that the [vi] Li –1 [vi] Fe 2+ [iv] Si –1 [iv] Al exchange vector produces a decrease in the lateral dimensions of the tetrahedral and octahedral sheets. The decrease in basal oxygen distances results from the effect of the strain caused by the orientation of opposing tetrahedral sheets within a 2:1 layer. The decrease reduces the strain so that the basal oxygen plane can remain nearly planar. Changes in these dimensions via distortions of the tetrahedral basal-oxygen ring (α = 3.3° and 4.1° for MLG-114 and Ch-140, respectively) are limited. Octahedral M1 and M3 sites are similar in size and much larger than M2 and the mean electron count is M3 〈 M1 〈 M2 in MLG-114 and M1 M2 〈 M3 in Ch-140. Al preferentially occupies the M2 site, whereas Fe and Li are nearly disordered between M1 and M3 sites with a slight preference of Fe for the M1 site in MLG-114 and for M3 site in Ch-140. Element concentrations on the (001) surface, obtained through X-ray photoelectron spectroscopy (XPS) high-resolution spectra for Si 2p , Al 2p , Fe 2p , K 2p , Li 1s , and F 1s core levels, indicate that a greater amount of lithium and a smaller amount of potassium characterize the surface with respect to the bulk. The decrease in K content, commonly observed in micas, is related to its location on the cleavage surface, because the cation must be distributed equally between the two (001) surfaces generated upon cleavage. The increase in Li content on or near the (001) cleavage surface suggests a preference for cleavage near lithium-enriched regions. The surface structure of the polylithionite crystals suggests that Al, Li, and Fe cations maintain coordination features at the surface similar to the bulk. Silicon, however, which is generally in fourfold coordination, shows also a small number of [1]-fold coordinated components at a binding energy of 99.85 eV.

Description: Agakhanovite-(Y), ideally (YCa) 2 KBe 3 Si 12 O 30 , is a new milarite-group mineral from the Heftetjern pegmatite, Tørdal, southern Norway. Crystals are prismatic along [001], and show the forms {100} and {100}. Agakhanovite-(Y) is colorless with a white streak and a vitreous luster, and does not fluoresce under ultraviolet light. There is no cleavage or parting, and no twinning was observed. Mohs hardness is 6, and agakhanovite-(Y) is brittle with a conchoidal fracture. The calculated density is 2.672 g/cm 3 . Optical properties were measured with the Bloss spindle stage for the wavelength 590 nm using a gel filter. Agakhanovite-(Y) is uniaxial (–) with indices of refraction = 1.567, = 1.564, both ±0.002; the calculated birefringence is 0.003 and it is non-pleochroic. Agakhanovite-(Y) is hexagonal, space group P 6/ mcc , a = 10.3476(2), c = 13.7610(3) Å, V = 1276.02(9) Å 3 , Z = 2, c:a = 1.330. The seven strongest lines in the X-ray powder-diffraction pattern are as follows: d (Å), I , ( hkl ): 2.865, 100, (24); 3.287, 96, (31); 4.134, 84, (22); 6.877, 56, (002); 2.986, 43, (030); 4.479, 38, (020); 2.728, 36, (024). Chemical analysis by electron microprobe gave SiO 2 69.56, Al 2 O 3 0.35, Y 2 O 3 9.69, Yb 2 O 3 0.15, FeO 0.02 CaO 5.75, Na 2 O 0.07, K 2 O 4.52, BeO(calc) 7.06, H 2 O(calc) 1.74, sum 98.91 wt%. The H 2 O content was determined by crystal-structure analysis. On the basis of 30 anions, the empirical formula is (Y 0.89 Yb 0.01 Ca 1.06 ) 1.96 (H 2 O) 0.92 Na 0.02 K 1.00 (Be 2.93 Al 0.07 ) 3.00 Si 12.02 O 30 . The crystal structure of agakhanovite-(Y) was refined to an R 1 index of 1.9% based on 660 unique observed reflections collected on a three-circle rotating-anode (Mo K α X-radiation) diffractometer equipped with multilayer optics and an APEX-II detector. In the end-member structure of agakhanovite-(Y), the A site is occupied equally by Y and Ca, and the B site is vacant; agakhanovite-(Y) is the Y-analog of oftedalite: ScCa 2 KBe 3 Si 12 O 30 , and the Y-Ca-Be analog of klöchite, (Fe 2+ Fe 3+ ) 2 KZn 3 Si 12 O 30 .

Description: We investigated the properties of Al-bearing SiO 2 (with 4 or 6 wt% Al 2 O 3 ) at pressures and temperatures corresponding to the lowermost mantle, using laser-heated diamond-anvil cell coupled with synchrotron-based in situ X-ray diffraction. The phase transition from CaCl 2 -structured to α-PbO 2 -structured (seifertite) polymorphs occurs between 113 and 119 GPa at 2500 K. The range of pressure where the two phases coexist is small. There is a slight decrease of the transition pressure with increasing Al-content. We propose a tentative phase diagram reporting the minerals composition as a function of pressure in the SiO 2 -Al 2 O 3 system. We also refine the P-V-T equation of state of Al-bearing seifertite based on volume measurements up to more than 160 GPa and 4000 K [ V 0 = 92.73(10) Å 3 , K 0 = 304.2(3.0) GPa, K ' 0 = 4.59 (fixed), D0 = 1130 K (fixed), 0 = 1.61(3)]. At 300 K, the volume decrease at the CaCl 2 to α-PbO 2 transition is 0.5(1)%, a value slightly lower than the 0.6% reported previously for Al-free samples. At high temperature, the Grüneisen parameter of seifertite is found to be similar to that of stishovite. Nevertheless, the V / V across the CaCl 2 -form to seifertite transition is found to increase slightly with increasing temperature. Across the phase transition, volume changes can be translated into density changes only when the Al substitution mechanisms in both CaCl 2 -form and seifertite are defined. The analysis of all available data sets suggests different substitution mechanisms for the two SiO 2 polymorphs. Al-substitution could occur via O-vacancies in the CaCl 2 -form and via extra interstitial Al in seifertite. This would result in a density increase of 2.2(3)% at 300 K for SiO 2 in basaltic lithologies. Alternatively, the same Al-substitution mechanism in both of the SiO 2 -dominated phases would yield a density increase of 0.5(1)%.