ALBERT

Description: Kornerupine, ({square}, Mg, Fe)(Al, Mg, Fe)9(Si, Al, B)5O21(OH, F), is known from only five mafic or ultramafic settings worldwide (of the 〉70 localities overall). We report a sixth occurrence from Akarui Point in the Lutzow-Holm Complex, East Antarctica, where two ruby corundum (0.22-0.34 wt% Cr2O3)-plagioclase lenses are found at the same structural level as boudinaged ultrabasic rocks in hornblende gneiss and amphibolite. Ion microprobe analyses of kornerupine give 13-59 ppm Be, 181-302 ppm Li, and 5466-6812 ppm B, corresponding to 0.38-0.47 B per 21.5 O; associated sapphirine also contains B (588-889 ppm). Peak metamorphic conditions are estimated to be 770-790 {degrees}C and 7.7-9.8 kbar. Kornerupine encloses tourmaline and plagioclase, which suggests the prograde reaction tourmaline (1) + plagioclase (〉An34)+ sapphirine{+/-}spinel[-〉]kornerupine+corundum (ruby)+plagioclase (〈An82){+/-}(fluid or melt). Alternatively, kornerupine and tourmaline could have formed sequentially under nearly constant P-T conditions during the infiltration of fluid that was originally B-bearing, but then progressively lost Na (or gained Ca) and B through reaction with mafic rocks. Kornerupine later reacted with H2O-CO2 fluid in cracks at P-T conditions in the andalusite stability field: kornerupine+plagioclase+(Na, K, {+/-} Si in fluid)[-〉]tourmaline+biotite+corundum (sapphire){+/-} magnesite{+/-}andalusite+(Ca in fluid). Secondary tourmaline differs from the included tourmaline in containing less Ti and having a higher Na/(Na+Ca+K) ratio. There are two possible scenarios for introducing B into the lenses: (1) infiltration of boron-bearing aqueous fluids released by prograde breakdown of muscovite in associated metasedimentary rocks; (2) hydrothermal alteration of mafic and ultramafic rocks by seawater prior to peak metamorphism. The latter scenario is consistent with an earlier suggestion that Akarui Point could be part of an ophiolite complex developed between the Yamato-Belgica and Rayner complexes.

Description: The Brattstrand Paragneiss, a highly deformed Neoproterozoic granulite-facies metasedimentary sequence, is cut by three generations of ~500 Ma pegmatite. The earliest recognizable pegmatite generation, synchronous with D 2–3 , forms irregular pods and veins up to a meter thick, which are either roughly concordant or crosscut S 2 and S 3 fabrics and are locally folded. Pegmatites of the second generation, D 4 , form planar, discordant veins up to 20–30 cm thick, whereas the youngest generation, post-D 4 , forms discordant veins and pods. Clear associations of pegmatites with broadly coeval granites are lacking. The D 2–3 and D 4 pegmatites are abyssal class (boron-beryllium subclass) characterized by graphic tourmaline + quartz intergrowths and boralsilite (Al 16 B 6 Si 2 O 37 ); the borosilicates prismatine, grandidierite, werdingite, and dumortierite are locally present. In contrast, post-D 4 pegmatites host tourmaline (but not in graphic intergrowths with quartz), beryl, and primary muscovite and are assigned to the muscovite-rare-element class. Spatial correlations between B-bearing pegmatites and B-rich units in the host Brattstrand Paragneiss are strongest for the D 2–3 pegmatites and weakest for the post-D 4 pegmatites, suggesting that the D 2–3 pegmatites may be closer to their source. Strontium-Nd-Pb isotope results for feldspars from nine pegmatites (three from each generation) indicate high and variable initial 87 Sr/ 86 Sr (0.7334–0.7870) and low Nd (–8.1 to –13.9). Nd tends to be highest in D 2–3 and lowest in post-D 4 pegmatites while 87 Sr/ 86 Sr shows similar ranges for all three generations. Initial 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios vary considerably (17.71–19.97, 15.67–15.91, 38.63–42.84), forming broadly linear arrays well above global Pb growth curves. The D 2–3 pegmatites contain the most radiogenic Pb, while the post-D 4 pegmatites have the least radiogenic Pb; data for D 4 pegmatites overlap with both groups. Broad positive correlations for Pb and Nd isotopic ratios could reflect source rock compositions controlled by two components. Component 1 ( 206 Pb/ 204 Pb ≥ 20, 208 Pb/ 204 Pb ≥ 43, Nd ≥ –8) most likely represents old upper crust with high U/Pb and very high Th/Pb. Component 2 ( 206 Pb/ 204 Pb ≤ 18, 208 Pb/ 204 Pb ~ 38.5, Nd500 –14 to –12) has a distinctive high- 207 Pb/ 206 Pb signature which evolved through dramatic lowering of U/Pb in crustal protoliths during a Neoproterozoic granulite-facies metamorphism. Component 1, represented in the locally derived D 2–3 pegmatites, probably reflects melt sources in biotite and borosilicate gneisses within the Brattstrand Paragneiss, which has a wide range of U/Pb and Th/Pb ratios and an inferred early Proterozoic crustal residence age. The Pb isotope signature of component 2, represented in the "far-from-source" post-D 4 pegmatites, resembles feldspar Pb isotope ratios in Cambrian granites intrusive into the Brattstrand Paragneiss. However, 87 Sr/ 86 Sr ratios in the pegmatites are much higher than in the granites, implying that the pegmatite melts are unlikely to be direct magmatic differentiates of the granites, although they may have broadly similar crustal sources. Temporal shifts in pegmatite source signatures, with a general sense of deeper crustal sources in the younger pegmatite generations, may reflect cooling of the crust after Cambrian metamorphism.

Description: Four factors contribute to the roles played by chance and necessity in determining mineral distribution and diversity at or near the surfaces of terrestrial planets: (1) crystal chemical characteristics; (2) mineral stability ranges; (3) the probability of occurrence for rare minerals; and (4) stellar and planetary stoichiometries in extrasolar systems. The most abundant elements generally have the largest numbers of mineral species, as modeled by relationships for Earth's upper continental crust (E) and the Moon (M), respectively: Log(NE)=0.22 Log(CE)+1.70(R2=0.34)(4861 minerals,72 elements) Log(NM)=0.19 Log(CM)+0.23(R2=0.68)(63 minerals,24 elements), where C is an element's abundance in ppm and N is the number of mineral species in which that element is essential. Several elements that plot significantly below the trend for Earth's upper continental crust ( e.g. , Ga, Hf, and Rb) mimic other more abundant elements and thus are less likely to form their own species. Other elements ( e.g ., Ag, As, Cu, Pb, S, and U) plot significantly above the trend, which we attribute to their unique crystal chemical affinities, multiple coordination and oxidation states, their extreme concentration in some ore-forming fluids, and/or frequent occurrence with a variety of other rare elements—all factors that increase the diversity of mineral species incorporating these elements. The corresponding diagram for the Moon shows a tighter fit, most likely because none of these elements, except Cu and S, are essential constituents in lunar minerals. Given the similar slopes for Earth and the Moon, we suggest that the increase in mineral diversity with element abundance is a deterministic aspect of planetary mineral diversity. Though based on a limited number of collecting sites, the Moon's observed mineralogical diversity could be close to the minimum for a rocky planet or moon comparable in size—a baseline against which diversity of other terrestrial planets and moons having radii in the same range as Earth and its Moon can be measured. Mineral-forming processes on the Moon are limited to igneous activity, meteor impacts, and the solar wind—processes that could affect any planet or moon. By contrast, other terrestrial planets and moons have been subjected to more varied physical, chemical, and (in the case of Earth) biological processes that can increase mineral diversity in both deterministic and stochastic ways. Total mineral diversity for different elements is not appreciably influenced by the relative stabilities of individual phases, e.g. , the broad pressure-temperature-composition stability ranges of cinnabar (HgS) and zircon (ZrSiO 4 ) do not significantly diminish the diversity of Hg or Zr minerals. Moreover, the significant expansion of near-surface redox conditions on Earth through the evolution of microbial oxygenic photosynthesis tripled the available composition space of Earth's near-surface environment, and resulted in a corresponding tripling of mineral diversity subsequent to atmospheric oxidation. Of 4933 approved mineral species, 34% are known from only one or two localities, and more than half are known from five or fewer localities. Statistical analysis of this frequency distribution suggests that thousands of other plausible rare mineral species await discovery or could have occurred at some point in Earth's history, only to be subsequently lost by burial, erosion, or subduction— i.e. , much of Earth's mineral diversity associated with rare species results from stochastic processes. Measurements of stellar stoichiometry reveal that stars can differ significantly from the Sun in relative abundances of rock-forming elements, which implies that bulk compositions of some extrasolar Earth-like planets likely differ significantly from those of Earth, particularly if the fractionation processes in evolving stellar nebulas and planetary differentiation are factored in. Comparison of Earth's upper continental crust and the Moon shows that differences in element ratios are reflected in ratios of mineral species containing these elements. In summary, although deterministic factors control the distribution of the most common rock-forming minerals in Earth's upper continental crust and on the Moon, stochastic processes play a significant role in the diversity of less common minerals. Were Earth's history to be replayed, and thousands of mineral species discovered and characterized anew, it is probable that many of those minerals would differ from species known today.

Description: The system B 2 O 3 -Al 2 O 3 -SiO 2 (BAS) includes two ternary phases occurring naturally, boromullite, Al 9 BSi 2 O 19 , and boralsilite, Al 16 B 6 Si 2 O 37 , as well as synthetic compounds structurally related to mullite. The new mineral vránaite, a third naturally occurring anhydrous ternary BAS phase, is found with albite and K-feldspar as a breakdown product of spodumene in the elbaite-subtype Manjaka granitic pegmatite, Sahatany Valley, Madagascar. Boralsilite also occurs in this association, although separately from vránaite; both minerals form rare aggregates of subparallel prisms up to 100 μm long. Optically, vránaite is biaxial (–), n α = 1.607(1), n β = 1.634(1), n = 1.637(1) (white light), 2 V x (calc) = 36.4°, X c ; Y a ; Z = b . An averaged analysis by EMP and LA-ICP-MS (Li, Be) gives (wt%) SiO 2 20.24, B 2 O 3 11.73, Al 2 O 3 64.77, BeO 1.03, MnO 0.01, FeO 0.13, Li 2 O 1.40, Sum 99.31. Raman spectroscopy in the 3000–4000 cm –1 region rules out the presence of significant OH or H 2 O. Vránaite is monoclinic, space group I 2/ m , a = 10.3832(12), b = 5.6682(7), c = 10.8228(12) Å, β = 90.106(11)°; V = 636.97(13) Å 3 , Z = 1. In the structure [ R 1 = 0.0416 for 550 F o 〉 4 F o ], chains of AlO 6 octahedra run parallel to [010] and are cross-linked by Si 2 O 7 disilicate groups, BO 3 triangles, and clusters of AlO 4 and two AlO 5 polyhedra. Two Al positions with fivefold coordination, Al4 and Al5, are too close to one another to be occupied simultaneously; their refined site-occupancy factors are 54% and 20% occupancy, respectively. Al5 is fivefold-coordinated Al when the Al9 site and both O9 sites are occupied, a situation giving a reasonable structure model as it explains why occupancies of the Al5 and O9 sites are almost equal. Bond valence calculations for the Al4 site suggest Li is likely to be sited here, whereas Be is most probably at the Al5 site. One of the nine O sites is only 20% occupied; this O9 site completes the coordination of the Al5 site and is located at the fourth corner of what could be a partially occupied BO 4 tetrahedron, in which case the B site is shifted out of the plane of the BO 3 triangle. However, this shift remains an inference as we have no evidence for a split position of the B atom. If all sites were filled (Al4 and Al5 to 50%), the formula becomes Al 16 B 4 Si 4 O 38 , close to Li 1.08 Be 0.47 Fe 0.02 Al 14.65 B 3.89 Si 3.88 O36.62 calculated from the analyses assuming cations sum to 24. The compatibility index based on the Gladstone-Dale relationship is 0.001 ("superior"). Assemblages with vránaite and boralsilite are inferred to represent initial reaction products of a residual liquid rich in Li, Be, Na, K, and B during a pressure and chemical quench, but at low H 2 O activities due to early melt contamination by carbonate in the host rocks. The two BAS phases are interpreted to have crystallized metastably in lieu of dumortierite in accordance with Ostwald Step Rule, possibly first as "boron mullite," then as monoclinic phases. The presence of such metastable phases is suggestive that pegmatites crystallize, at least partially, by disequilibrium processes, with significant undercooling, and at high viscosities, which limit diffusion rates.

Description: Fontarnauite was discovered in cores recovered from the Kütahya-Emet 2 and 188 (named here as Doğanlar) boreholes drilled in the Emet borate basin near the village of Doğanlar, Kütahya Province, Western Anatolia, Turkey. The Emet (or Emet-Hisarcık) basin is one of the Neogene basins in western Turkey bearing a borate-rich unit intercalated with Miocene sediments. Fontarnauite is most commonly associated with probertite, glauberite, and celestine and occurs as isolated colorless to light-brown prismatic crystals or as clusters of crystals less than 5 mm long. Fontarnauite is brittle, with a Mohs hardness of 21/2–3, and perfect {010} cleavage. D calc = 2.533 g/cm 3 . The new mineral is optically biaxial (–), α 1.517(2), β 1.539(2), 1.543(2) (590 nm); 2 V meas = 46(1)°; 2 V calc = 46°; X ^ a 95.0° (β obtuse); Y // b , Z ^ c 81.9° (β acute). Dispersion is r 〉 v , medium to weak. The chemical composition (electron microprobe; B and H from the crystal-structure refinement) is as follows: SO 3 17.75, B 2 O 3 38.66, CaO 2.26, SrO 18.98, Na 2 O 12.65, K 2 O 1.70, H 2 O 10.01, total 102.01 wt.%. The empirical formula (based on 15 O atoms per formula unit) is (Na 1.84 K 0.16 ) 2.00 (Sr 0.82 Ca 0.18 ) 1.00 S 1.00 B 5 H 5 O 15 ; the endmember formula is Na 2 Sr(SO 4 ) [B 5 O 8 (OH)](H 2 O) 2 based on the crystal-structure refinement. Single-crystal X-ray studies gave the space group P 2 1 /c, a 6.458(2), b 22.299(7), c 8.571(2) Å, β 103.047(13)°, V 1202.5(1.0) Å 3 , Z = 4. Structure refinement ( R 1 = 2.9%) revealed that two BO 4 tetrahedra and three BO 3 triangles share vertices to form B 5 O 10 (OH) units that link to other B 5 O 10 (OH) units along [100] and [001] to give a [B 5 O 8 (OH)] sheet parallel to (010). Within the central cavities of opposing sheets are the H 2 O groups, SO 4 tetrahedra, and Na (1) sites; the Sr and Na (2) sites occupy the interstices of a given sheet. The region of the structure where opposing cusps of neighboring sheets approach each other is dominated by weaker H-bonding associated with the OH and H 2 O groups, in accord with the observed perfect {010} cleavage. The strongest lines in the powder X-ray diffraction pattern, obtained after profile fitting using the Le Bail method, are as follows [ d in Å ( I ) ( hkl )]: 11.1498 (100)(020), 3.3948 (8)(061), 3.3389 (20)(042), 3.1993, 3.1990 (10)(160, 1 42), 3.0458(10)(052), 3.0250(7)(220), 2.7500 (10)( 2 22,142), 2.3999 (8)(260), 2.2300, 2.2284(7)(0 10 0,222), 1.9241, 1.9237(7)(311, 2 24). The holotype is deposited in the mineralogy collection of the Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada, accession number M56745.

Description: The Szklary holtite is represented by three compositional varieties: (1) Ta-bearing (up to 14.66 wt.% Ta2O5), which forms homogeneous crystals and cores within zoned crystals; (2) Ti-bearing (up to 3.82 wt.% TiO2), found as small domains within the core; and (3) Nb-bearing (up to 5.30 wt.% Nb2O5,) forming the rims of zoned crystals. All three varieties show variable Sb+As content, reaching 19.18 wt.% Sb2O3 (0.87 Sb a.p.f.u.) and 3.30 wt.% As2O3 (0.22 As a.p.f.u.) in zoned Ta-bearing holtite, which constitutes the largest Sb+As content reported for the mineral. The zoning in holtite is a result of Ta-Nb fractionation in the parental pegmatite-forming melt together with contamination of the relatively thin Szklary dyke by Fe, Mg and Ti. Holtite and the As- and Sb-bearing dumortierite, which in places overgrows the youngest Nb-bearing zone, suggest the following crystallization sequence: Ta-bearing holtite [-〉] Ti-bearing holtite [-〉] Nb-bearing holtite [-〉] As- and Sb-bearing, (Ta,Nb,Ti)-poor dumortierite [-〉] As- and Sb-dominant, (Ta,Nb,Ti)-free dumortierite-like mineral (16.81 wt.% As2O3 and 10.23 wt.% Sb2O3) with (As+Sb) 〉 Si. The last phase is potentially a new mineral species, Al6{square}B(Sb,As)3O15, or Al5{square}2B(Sb,As)3O12(OH)3, belonging to the dumortierite group. The Szklary holtite shows no evidence of clustering of compositions around `holtite I' and `holtite II'. Instead, the substitutions of Si4+ by Sb3++As3+ at the Si/Sb sites and of Ta5+ by Nb5+ or Ti4+ at the Al(1) site suggest possible solid solutions between: (1) (Sb,As)-poor and (Sb,As)-rich holtite; (2) dumortierite and the unnamed (As+Sb)-dominant dumortierite-like mineral; and (3) Ti-bearing dumortierite and holtite, i.e. our data provide further evidence for miscibility between holtite and dumortierite, but leave open the question of defining the distinction between them. The Szklary holtite crystallized from the melt along with other primary Ta-Nb-(Ti) minerals such as columbite-(Mn), tantalite-(Mn), stibiotantalite and stibiocolumbite as the availability of Ta decreased. The origin of the parental melt can be related to anatexis in the adjacent Sowie Mountains complex, leading to widespread migmatization and metamorphic segregation in pelitic-psammitic sediments metamorphosed at [~]390-380 Ma.

Description: Recent studies of mineral diversity and distribution lead to the prediction of 〉1563 mineral species on Earth today that have yet to be described—approximately one fourth of the 6394 estimated total mineralogical diversity. The distribution of these "missing" minerals is not uniform with respect to their essential chemical elements. Of 15 geochemically diverse elements (Al, B, C, Cr, Cu, Mg, Na, Ni, P, S, Si, Ta, Te, U, and V), we predict that approximately 25% of the minerals of Al, B, C, Cr, P, Si, and Ta remain to be described—a percentage similar to that predicted for all minerals. Almost 35% of the minerals of Na are predicted to be undiscovered, a situation resulting from more than 50% of Na minerals being white, poorly crystallized, and/or water soluble, and thus easily overlooked. In contrast, we predict that fewer than 20% of the minerals of Cu, Mg, Ni, S, Te, U, and V remain to be discovered. In addition to the economic value of most of these elements, their minerals tend to be brightly colored and/or well crystallized, and thus likely to draw attention and interest. These disparities in percentages of undiscovered minerals reflect not only natural processes, but also sociological factors in the search, discovery, and description of mineral species.

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.