ALBERT

Description: We conducted 1 atm experiments on a synthetic Hawaiian picrite at f O 2 values ranging from the quartz–fayalite–magnetite (QFM) buffer to air and temperatures ranging from 1302 to 1600°C. Along the QFM buffer, olivine is the liquidus phase at ~1540°C and small amounts of spinel (〈 0·2 wt %) are present in experiments conducted at and below 1350°C. The olivine becomes progressively more ferrous with decreasing temperature [Fo 92 · 3 to Fo 87 · 3 , where Fo = 100 x Mg/(Mg + Fe), atomic]; compositions of coexisting liquids reflect the mode and composition of the olivine with concentrations of SiO 2 , TiO 2 , Al 2 O 3 , and CaO increasing monotonically with decreasing temperature, those of NiO and MgO decreasing, and FeO* (all Fe as FeO) remaining roughly constant. An empirical relationship based on our data, T (°C) = 19·2 x (MgO in liquid, wt %) + 1048, provides a semi-quantitative geothermometer applicable to a range of Hawaiian magma compositions. The olivine–liquid exchange coefficient, = (FeO/MgO) ol /(FeO/MgO) liq , is 0·345 ± 0·009 (1 ) for our 11 experiments. A literature database of 446 1 atm experiments conducted within 0·25 log units of the QFM buffer (QFM ± 0·25) yields a median of 0·34; values from single experiments range from 0·41 to 0·13 and are correlated with SiO 2 and alkalis in the liquid, as well as the forsterite (Fo) content of the olivine. For 78 experiments with broadly tholeiitic liquid compositions (46–52 wt % SiO 2 and ≤ 3 wt % Na 2 O + K 2 O) coexisting with Fo 92 – 80 olivines, and run near QFM (QFM ± 0·25), is approximately independent of composition with a median value of 0·340 ± 0·012 (error is the mean absolute deviation of the 78 olivine–glass pairs from the database that meet these compositional criteria), a value close to the mean value of 0·343 ± 0·008 from our QFM experiments. Thus, over the composition range encompassed by Hawaiian tholeiitic lavas and their parental melts, ~ 0·34 and, given the redox conditions and a Fo content for the most magnesian olivine phenocrysts, a parental melt composition can be reconstructed. The calculated compositions of the parental melts are sensitive to the input parameters, decreasing by ~1 wt % MgO for every log unit increase in the selected f O 2 , every 0·5 decrease in the Fo-number of the target olivine, and every 0·015 decrease in . For plausible ranges in redox conditions and Fo-number of the most MgO-rich olivine phenocrysts, the parental liquids for Hawaiian tholeiites are highly magnesian, in the range of 19–21 wt % MgO for Kilauea, Mauna Loa and Mauna Kea.

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: Browneite (IMA 2012-008), MnS, is a new member of the sphalerite group, discovered in Zaklodzie, an ungrouped enstatite-rich achondrite. The type material occurs as one single crystal (~16 μm in size) in contact with and surrounded by plagioclase; enstatite and troilite are nearby. Low-Ni iron, martensitic iron, tridymite, quartz, cristobalite, sinoite, schreibersite, buseckite, keilite, and graphite, are also present in the type sample. Browneite is yellowish brown and translucent. The mean chemical composition, as determined by electron microprobe analysis of the type material, is (wt%) S 36.46, Mn 62.31, Fe 0.62, Ca 0.10, sum 99.49, leading to an empirical formula calculated on the basis of 2 atoms of (Mn 0.993 Fe 0.010 Ca 0.002 )S 0.995 . Electron back-scatter diffraction patterns of browneite are a good match to that of synthetic β-MnS with the F 3 m structure, showing a = 5.601 Å, V = 175.71 Å 3 , and Z = 4. Browneite is a low-temperature (〈200 °C) phase, metastable relative to alabandite, that postdates the impact melting and subsequent crystallization of an enstatite-rich rock.

Description: Majindeite (IMA 2012-079), Mg 2 Mo 3 O 8 , is a new mineral, occurring as submicrometer-sized crystals with Ni-Fe and Ru-Os-Ir alloys, ± apatite and Nb-oxide. The observed assemblages are partially or wholly enclosed by MgAl 2 O 4 spinel in a Type B1 Ca-Al-rich inclusion, ACM-2 , from the Allende CV3 carbonaceous chondrite. The type majindeite has an empirical formula of (Mg 1.57 Fe 0.43 )Mo 3.00 O 8 , and a nolanite-type P 6 3 mc structure with a = 5.778 Å, c = 9.904 Å, V = 286.35 Å 3 , and Z = 2, leading to a calculated density of 5.54 g/cm 3 . Majindeite likely formed during the subsolidus oxidation of Mo-rich precursor phase(s) included in Fe-Ni rich alloys in a system that was open to O, Mg, and Ca, which were derived externally and introduced via cracks, subgrain boundaries, and/or surfaces exposed at the exterior of the spinel. If magnetite existed in the phase assemblage, it was lost due to Fe volatilization prior to the formation of majindeite. The immediate precursor to majindeite was likely kamiokite. Majindeite formed during an oxidation event contemporaneous with or postdating the formation of grossular-rich veins in melilite. Kamiokite, the Fe-rich analog of majindeite, also occurs in ACM-2 but only within phase assemblages that contain magnetite and which are entirely enclosed in melilite ± alteration products. Here, grossular-rich veins are not observed and the coexisting awaruites are more Fe-rich than those observed with majindeite. As with majindeite, the precursors for kamiokite grains were also likely to have been Mo-rich alloys, but the Mo-oxide remained magnetite-saturated throughout the alteration process and therefore remained Fe-rich.

Description: We measured Ni partitioning between olivine and melt, , in experiments on mid-ocean ridge basalt (MORB) encapsulated in olivine at pressures from 1 atm to 3·0 GPa and temperatures from 1400 to 1550°C. We present a series of experiments where the temperature ( T ) at each pressure ( P ) was selected so that the liquid composition remained approximately constant over the entire P–T range. This approach allowed us to investigate the effects of T and P on , independent of substantial changes in liquid composition. Our experiments show that for a liquid with ~18 wt % MgO, decreases from 5·0 to 3·8 as the temperature increases from 1400 to 1550°C. Fitting our experimental results and literature data to thermodynamic expressions for as a function of both temperature and liquid composition shows that the small variations in liquid composition in our experiments account for little of the observed variation of . Because the changes in volume and heat capacity of the exchange reaction are small, , the Ni partition coefficient on a molar basis, is well described by with = 4375 K and = –2·023 for our data ( = 4338 K and = –1·956 for our experiments combined with a compilation of literature data). This expression is easy to use and applicable to a wide range of pressures, temperatures, and phase compositions. Based on our results and data from the literature, the temperature dependence of leads to the prediction that when a deep partial melt from a peridotitic mantle source is brought to low pressure and cooled, the first Mg-rich olivines to crystallize can have significantly higher NiO contents than those in the residual source from which the melt was extracted. This enrichment in Ni is driven by the difference between the temperature of low-pressure crystallization and the temperature of melt extraction from the residue. The average observed enrichment of Ni in forsteritic olivine phenocrysts from Hawaii—relative to the typical olivines from mantle peridotites—is consistent with a simple scenario of high-temperature partial melting of an olivine-bearing source at the base of the lithosphere followed by low-temperature crystallization of olivine. The most extreme enrichments of Ni in Hawaiian olivine phenocrysts and the lower Ni contents of some olivines can also be explained by the known variability of Ni contents of olivines from mantle peridotites via the same simple scenario. Although we cannot rule out alternative hypotheses for producing the high-Ni olivines observed in Hawaii and elsewhere, these processes or materials are unnecessary to account for NiO enrichments in olivine. The absolute temperature, in addition to the difference between the temperature of melt segregation from the residue and the temperature of low-pressure crystallization, is a significant factor in determining the degree of Ni enrichment in olivine phenocrysts relative to the olivines in the mantle source. The moderate Ni enrichment observed in most komatiitic olivines compared with those of Hawaii may result from the higher absolute temperatures required to generate MgO-rich komatiitic melts. Observed NiO enrichments in early crystallizing komatiitic olivine are consistent with their high temperatures of crystallization and with a deep origin for the komatiite parental melts.

Description: Kangite (IMA 2011-092), (Sc,Ti,Al,Zr,Mg,Ca,) 2 O 3 , is a new scandia mineral, occurring as micrometer-sized crystals with REE-rich perovskite and spinel in a davisite-dominant ultra-refractory inclusion from the Allende CV3 carbonaceous chondrite. The phase was characterized by SEM, EBSD, synchrotron micro-Laue diffraction, micro-Raman, and EPMA. The mean chemical composition of the type kangite is (wt%) TiO 2 36.6, Sc 2 O 3 26.4, ZrO 2 11.3, Al 2 O 3 7.0, Y 2 O 3 5.4, CaO 3.9, MgO 3.14, Dy 2 O 3 1.8, SiO 2 1.7, V 2 O 3 1.31, Er 2 O 3 0.92, FeO 0.8, Gd 2 O 3 0.60, Ho 2 O 3 0.40, Tb 2 O 3 0.18, Cr 2 O 3 0.09, ThO 2 0.04, O –0.3, sum 101.28, which leads to an empirical formula calculated on the basis of 3 O atoms of [(Sc 0.54 Al 0.16 Y 0.07 V 0.03 Gd 0.01 Dy 0.01 Er 0.01 ) 3+ 0.83 (Ti 0.66 Zr 0.13 ) 4+ 0.79 (Mg 0.11 Ca 0.06 Fe 0.02 ) 2+ 0.19 0.19 ] 2.00 O 3 . Synchrotron micro-Laue diffraction (i.e., an energy scan by a high-flux X-ray monochromatic beam) on one type domain at submicrometer resolution revealed that kangite has a cation-deficient Ia bixbyite-type cubic structure. The cell parameters are a = 9.842(1) Å, V = 953.3(1) Å 3 , Z = 16, which leads to a calculated density of 3.879 g/cm 3 . Kangite is a new ultra-refractory mineral, likely originating through low-temperature oxidation of a Sc-,Ti 3+ -enriched high-temperature condensate oxide dating to the birth of the Solar System.

Description: Monipite (IMA 2007-033), MoNiP, is a new phosphide mineral that occurs as one 1 x 2 μm crystal in a Type B1 Ca-Al-rich inclusion (CAI) ACM-2 from the Allende CV3 carbonaceous chondrite. It has an empirical formula of (Mo 0.84 Fe 0.06 Co 0.04 Rh 0.03 )(Ni 0.89 Ru 0.09 )P, and a P 2 m Fe 2 P type structure with a = 5.861, c = 3.704 Å, V = 110.19 Å 3 , and Z = 3. The calculated density using our measured composition is 8.27 g/cm 3 , making monipite the densest known mineral phosphide. Monipite probably either crystallized from an immiscible P-rich melt that had exsolved from an Fe-Ni-enriched alloy melt that formed during melting of the host CAI or it exsolved from a solidified alloy. Most of the original phosphide in the type occurrence was later altered to apatite and Mo-oxides, leaving only a small residual grain. Monipite occurs within an opaque assemblage included in melilite that contains kamiokite (Fe 2 Mo 3 O 8 ), tugarinovite (MoO 2 ), and a Nb-rich oxide [(Nb,V,Fe)O 2 ], none of which has previously been reported in meteorites, together with apatite, awaruite (Ni 2 Fe), and vanadian magnetite.