Volume 107, Issue 12

The Nanyangshan Li-Cs-Ta (LCT) pegmatite is the largest of hundreds of pegmatite dikes in the eastern Qinling orogenic district, North China. The Nanyangshan pegmatite is strongly zoned into a contact zone, border zone, wall zone, intermediate zone, and core, with Li mineralization occurring predominantly in the intermediate zone. Inward through the intermediate zone, Li mineralization is divided into subzones of Spd (spodumene), Mbs (montebrasite), Elb (elbaite), and Lpd (lepidolite). Lithium minerals include spodumene, montebrasite, lithiophilite, elbaite, lepidolite, and possible former petalite. Paragenetic assemblages of Li minerals are variable, with spodumene ± Li-phosphates (montebrasite and lithiophilite), Fe-rich elbaite, lepidolite, and possible former petalite in the Spd subzone; Li-phosphates (main montebrasite and rare lithiophilite) + spodumene + Fe-bearing elbaite + lepidolite in the Mbs subzone; Fe-poor elbaite + lepidolite ± montebrasite in the Elb subzone; and lepidolite ± Fe-poor elbaite in the Lpd subzone. Whole-rock contents of Li 2 O, P 2 O 5 , B 2 O 3 , and F are consistent with the high contents of various Li minerals. Spodumene was formed first and dominantly from a Li-saturated melt in the Spd subzone (1.66 wt% Li 2 O). This subzone graduates into the P-rich Mbs subzone (3.75 wt% P 2 O 5 ) with montebrasite gradually succeeding Li-aluminosilicates, followed by the appearance of abundant Fe-poor elbaite in the Elb subzone (1.04 wt% B 2 O 3 ), reflecting the consumption of P in the melt. Lepidolite formed after early-formed Li phases in the F-rich Lpd subzone (2.03 wt% F), as indicated by replacement textures. Among the numerous LCT pegmatites worldwide, the Li mineralization sequence can be suggested as Li-aluminosilicates (commonly spodumene and less commonly petalite) → Li-phosphates (montebrasite-amblygonite and triphylite-lithiophilite) → elbaite → lepidolite, and can be regarded as a general sequence for Li mineralization.

Tomiolloite (IMA2021-019) is a new aluminum tellurite sulfite-sulfate mineral discovered at the Bambolla mine, Moctezuma, Sonora, Mexico, a well-known tellurium (Te) mineral locality. Tomiolloite forms roughly spherical clusters of crystals comprised of very thin, needle-like crystals (1 μm diameter, ~40 μm length) around a core of small, stubbier, broken crystals. Tomiolloite is generally found growing on tellurite or quartz. The strongest powder X‑ray diffraction lines are [ d obs Å ( I obs ) ( hkl )]: 11.667 (89) (100), 8.240 (38) (101), 4.107 (29) (202,211,121), 3.223 (100) (203,302,130), and 2.905 (37) (213,123,222,400). The empirical formula of tomiolloite, as determined by electron microprobe analysis, is (Al 10.64 Te 6 1.01 + Fe 3 0.31 + Zn 0.04 ) Σ12 (Te 4 5.00 + Pb 0.02 ) Σ5.02 (S 4 0.49 + S 6 0.49 + Si 0.02 ) Σ1.00 O 21.53 [(OH) 20.86 Cl 0.11 ] Σ20.97 , which is simplified to the ideal formula Al 12 (Te 4+ O 3 ) 5 [(SO 3 ) 0.5 (SO 4 ) 0.5 ](OH) 24 . Significant Te 6+ substitution for Al 3+ is observed in tomiolloite, verified by X‑ray photoelectron spectroscopy and crystal-structure analysis. The structure of tomiolloite was determined using synchrotron single-crystal X‑ray diffraction, showing that tomiolloite is hexagonal and crystallizes in the space-group P 63/ m , with the unit-cell parameters a = 13.3360(19) Å, c = 11.604(2) Å, V = 1787.3(6) Å 3 , and Z = 2. Tomiolloite has a unique microporous framework structure, which bears a slight similarity to that of zemannite, but it has a much larger cavity diameter (8.85 Å). The framework is built from edge-sharing M φ6 octahedra ( M = Al 3+ and Te 6+ ), Te 4+ O 3 trigonal pyramids, and Te 4+ O 4 disphenoids. M φ6 octahedra edge-share to form crankshaft-shaped chains along c , with Te 4+ O n polyhedra filling notches in the crankshafts and providing linkages between adjacent chains. The framework has an overall positive charge, which is balanced by the presence of both sulfite (SO 3 2− ) trigonal pyramids and sulfate (SO 4 2− ) tetrahedra in the channels.

Titanium (Ti) has long been considered to be immobile during weathering and diagenetic processes, and it is widely used for the normalization of elemental concentrations in weathering profiles. However, our study demonstrates that authigenic titania is commonly formed in fine-grained siliciclastics of a wide variety of facies through weathering of Ti-bearing silicates, authigenic euhedral anatase is present ubiquitously as nanoparticles, and its morphology varies in a predictable manner over a range of depositional environments. The crystal habit of authigenic anatase nanoparticles is controlled primarily by porewater pH during the early diagenetic alteration of Ti-bearing silicates. Authigenic anatase nanoparticles exhibit a distinct tetragonal tabular morphology in deep-marine facies, a tetragonal bipyramidal shape in shallow-marine facies, an irregular morphology with sponge-like aggregates in terrestrial-marine transitional to paludal facies, and euhedral short tetragonal prisms in lacustrine facies. Also, authigenic anatase is observed to form in organic-free glacial deposits, attesting its formation as an inorganic precipitate and demonstrating diagenetic remobilization of titanium in the absence of organic matter. Our findings suggest that authigenic anatase could be a sensitive proxy for the sedimentary environment and sedimentary porewater chemistry, and it will likely prove useful in depositional facies analysis.

The optical properties (scattering, absorption, and extinction) of spheroidal Cu particles embedded in intermediate plagioclase feldspar are computed for various sizes and shapes using the Mie theory and T-matrix method. The observed color for Cu-bearing plagioclase, as a function of particle size and shape, is also calculated from the computed extinction spectra. The colors and pleochroism observed in natural and treated Cu-bearing plagioclase can be explained from the computational results. The enigmatic green colors in some precious Oregon sunstones result from red light being scattered away by Cu nanoparticles of certain sizes. The UV-VIS spectra are collected on Cu-bearing plagioclase samples for comparison with the computational results, which are shown to match the optical observations. The results from this work may be used to quantify the concentration of colloidal Cu in plagioclase or glass with a similar refractive index. Particle sizes and shapes can also be characterized using extinction and scattering spectra, which can be collected with different optical configurations. New materials with special color effects and optical characteristics may be designed and engineered by applying the unusual properties of metal colloids.

Polekhovskyite, MoNiP 2 , is the first terrestrial Mo phosphide, a phosphorus-rich homolog of meteoritic monipite, MoNiP. The mineral represents a novel phosphide type of terrestrial Mo speciation. It was discovered among phosphide assemblages in pyrometamorphic rocks of the Hatrurim Formation (the Mottled Zone) in Israel, the area confined to the Dead Sea Transform fault system. Polekhovskyite occurs in the altered diopside microbreccia, as micrometer-sized euhedral crystals intimately intergrown with murashkoite, FeP and transjordanite, Ni 2 P, in association with Si-rich fluorapatite, hematite, and magnetite. In reflected light, the mineral has a bluish-gray color with no observable bireflectance and anisotropy. Chemical composition (electron microprobe, wt%): Mo 44.10, Ni 22.73, Fe 4.60, P 29.02, total 100.45, which corresponds to the empirical formula Mo 0.99 (Ni 0.83 Fe 0.18 ) 1.01 P 2.01 and leads to the calculated density of 6.626 g/cm. Polekhovskyite is hexagonal, space group P 63/ mmc , a = 3.330(1), c = 11.227(4) Å, V = 107.82(8) Å 3 , and Z = 2. The crystal structure has been solved and refined to R 1 = 0.0431 based on 50 unique observed reflections. The occurrence of Mo-bearing phosphides at the Dead Sea Transform area is a regional-scale phenomenon, with the localities tracked across both Israel and Jordan sides of the Dead Sea. The possible sources of Mo required for the formation of Mo-bearing phosphides are herein reviewed; they are likely related to the processes of formation of the Dead Sea Transform fault system. The problem of anthropogenic contamination of geological samples with Mo and Ni is also discussed in the paper in the context of the general aspects of discrimination between natural and technogenic ultra-reduced phases.

Brillouin spectroscopy at room temperature and pressures up to 40 GPa documents nearly identical elasticity and refractive index of amorphous CaSiO 3 created by two different methods: temperature-quenching the melt at ambient pressure and pressure-amorphizing crystalline wollastonite at room temperature. We find reproducible hysteresis of 0 to 8% on pressure cycling that is small relative to the 30 to 60% changes in shear and longitudinal wave velocities over this pressure range. Together with observed changes in refractive index and previous results from Raman spectroscopy, these measurements reveal a continuous and reversible change in atomic packing induced by pressure. Unlike many other silicate glasses, amorphous CaSiO 3 exhibits highly reproducible properties, behaving smoothly and reversibly under pressure cycling and possessing similar structure and elasticity regardless of synthesis paths for the starting material, which suggests that the amorphous solid may mimic the liquid over the pressure range investigated.

Nickel and cobalt arsenides, sulfarsenides, and sulfides occur in many hydrothermal ore deposits, but their thermodynamic properties are not well known, in some cases not known at all. In this work, we determined a full set of thermodynamic properties for heazlewoodite and skutterudite. Both phases were synthesized in evacuated silica tubes at elevated temperatures, and electron microprobe analyses gave their compositions as Ni 3 S 2 and CoAs 2.92 , respectively. Enthalpies of formation were measured by high-temperature oxide-melt solution calorimetry. The reference phases were pure elements, thus eliminating any systematic errors related to such phases. The enthalpies of formation at T = 298.15 K and P = 10 5 Pa are –216.0 ± 8.4(2σ) and –88.2 ± 6.1 kJ·mol −1 for Ni 3 S 2 and CoAs 2.92 , respectively. Entropies were calculated from low-temperature heat capacity ( C P ) data from relaxation (PPMS) calorimetry and are 133.8 ± 1.6 and 106.4 ± 1.3 J·mol –1 ·K –1 , respectively. The calculated Gibbs free energies of formation are –210.0 ± 8.4 and –79.9 ± 6.2 kJ·mol −1 for Ni 3 S 2 and CoAs 2.92 , respectively. The PPMS C P data, together with a set of differential scanning calorimetry measurements, were used to derive C P polynomials up to 700 K with the Kiefer model based on previously published frequencies of acoustic and optic modes. Equilibrium constants for selected reactions with an aqueous phase were calculated up to 700 K. Geochemical modeling in these systems, however, should await until more reliable data for other phases from the system Co-Ni-As-S are available.

Melting relations in the MgSiO 3 -SiO 2 system have been investigated at 13.5 GPa using a Kawai-type multi-anvil apparatus. The system displays eutectic melting with the eutectic point located at SiO 2 /(SiO 2 +MgO) = 0.61 (in mol; which is denoted by X Si hereafter) and at 2350 ± 50 °C. Taking into account the eutectic compositions at lower pressures reported in previous studies, i.e., 0.556 at 1 GPa (Hudon et al. 2005) and 0.60 at 5 GPa (Dalton and Presnall 1997), the eutectic composition is slightly enriched in SiO 2 with increasing pressure. The silica-rich eutectic composition is not consistent with the present peridotitic mantle composition ( X Si = 0.43). Considering Si incorporation into iron alloys in a magma ocean, however, mass-balance calculations based on an E-chondrite model demonstrate that the silicate magma ocean could have X Si consistent with the present peridotitic mantle.

Studying the structural evolution of the dolomite group at high pressure is crucial for constraining the deep carbon cycle and mantle dynamics. Here we collected high-pressure laser Raman spectra of natural Mg-dolomite CaMg(CO 3 ) 2 and Mn-dolomite kutnohorite Ca 1.11 Mn 0.89 (CO 3 ) 2 samples up to 56 GPa at room temperature in a diamond-anvil cell (DAC) using helium and neon as a pressure-transmitting medium (PTM), respectively. Using helium or neon can ensure samples stay under relatively hydrostatic conditions over the investigated pressure range, resembling the hydrostatic conditions of the deep mantle. Phase transitions in CaMg(CO 3 ) 2 were observed at 36.1(25) GPa in helium and 35.2(10) GPa in neon PTM from dolomite-II to -III, respectively. Moreover, the onset pressure of Mn-dolomite Ca 1.11 Mn 0.89 (CO 3 ) 2 -III occurs at 23−25 GPa, about 10 GPa lower than that of Mg-dolomite-III, suggesting that cation substitution could significantly change the onset pressure of the phase transitions in the dolomite group. These results provide new insights into deep carbon carriers within the Earth’s mantle.

Bastnäsite [REE(CO 3 )F] is the main mineral of REE ore deposits in carbonatites. Synthetic bastnäsite-like compounds were precipitated from aqueous solutions by many different methods, but previous attempts to model magmatic crystallization of bastnäsite from hydrous calciocarbonatite melts were unsuccessful. Here we present the first experimental evidence that bastnäsite and two other REE carbonates, burbankite, and lukechangite, can crystallize from carbonatite melt in the synthetic system La(CO 3 )F-CaCO 3 -Na 2 CO 3 at temperatures between 580 and 850 °C and a pressure 100 MPa. The experiments on starting mixtures of reagent-grade CaCO 3 , Na 2 CO 3 , La 2 (CO 3 ) 3 , and LaF 3 were carried out in cold-seal rapid-quench pressure vessels. The studied system is an isobaric pseudoternary join of a quinary system where CO 2 and fluorides act as independent components. Liquidus phases in the run products are calcite, nyerereite, Na carbonate, bastnäsite, burbankite solid solution (Na,Ca) 3 (Ca,La) 3 (CO 3 ) 5 , and lukechangite Na 3 La 2 (CO 3 ) 4 F. Calcite and bastnäsite form a eutectic in the boundary join La(CO 3 )F-CaCO 3 at 780 ± 20 °C and 58 wt% La(CO 3 )F. Phase equilibria in the boundary join La(CO 3 )F-Na 2 CO 3 are complicated by peritectic reaction between Ca-free end-member of burbankite solid solution petersenite (Pet) and lukechangite (Luk) with liquid (L): N a 4 L a 2 C O 3 5 ( P e t ) + N a F ( L ) = N a 3 L a 2 C O 3 4   F ( L u k ) + N a 2 C O 3 ( N c ) . $$ \begin{equation} \mathrm{Na}_4 \mathrm{La}_2\left(\mathrm{CO}_3\right)_5(\mathrm{Pet})+\mathrm{NaF}(\mathrm{L})=\mathrm{Na}_3 \mathrm{La}_2\left(\mathrm{CO}_3\right)_4 \mathrm{~F}(\mathrm{Luk})+\mathrm{Na}_2 \mathrm{CO}_3(\mathrm{Nc}) . \end{equation}$$ The right-hand-side assemblage becomes stable below 600 ± 20 °C. In ternary mixtures, bastnäsite (Bst), burbankite (Bur), and calcite (Cc) are involved in another peritectic reaction: 2 L a C O 3 F ( B s t ) + C a C O 3 ( C c ) + 2 N a 2 C O 3 (   L ) = N a 2 C a L a 2 C O 3 5 ( B u r ) + 2 N a F ( L ) . $$\begin{equation} 2 \mathrm{La}\left(\mathrm{CO}_3\right) \mathrm{F}(\mathrm{Bst})+\mathrm{CaCO}_3(\mathrm{Cc})+2 \mathrm{Na}_2 \mathrm{CO}_3(\mathrm{~L})=\mathrm{Na}_2 \mathrm{CaLa}_2\left(\mathrm{CO}_3\right)_5(\mathrm{Bur})+2 \mathrm{NaF}(\mathrm{L}) . \end{equation}$$ Burbankite in equilibrium with calcite replaces bastnäsite below 730 ± 20 °C. Stable solidus assemblages in the pseudoternary system are: basnäsite-burbankite-fluorite-calcite, basnäsite-burbankite-fluorite-lukechangite, bastnäsite-burbankite-lukechangite, burbankite-lukechangite-nyerereitecalcite, and burbankite-lukechangite-nyerereite-natrite. Addition of 10 wt% Ca 3 (PO 4 ) 2 to one of the ternary mixtures resulted in massive crystallization of La-bearing apatite and monazite and complete disappearance of bastnäsite and burbankite. Our results confirm that REE-bearing phosphates are much more stable than carbonates and fluorocarbonates. Therefore, primary crystallization of the latter from common carbonatite magmas is unlikely. Possible exceptions are carbonatites at Mountain Pass that are characterized by very low P 2 O 5 concentrations (usually at or below 0.5 wt%) and extremely high REE contents in the order of a few weight percent or more. In other carbonatites, bastnäsite and burbankite probably crystallized from highly concentrated alkaline carbonate-chloride brines that were found in melt inclusions and are thought to be responsible for widespread fenitization around carbonatite bodies.

The euhedral shapes of pyrite FeS 2 are usually exposing three main surfaces: striated (001), smooth (111), and striated (210), leading to the cubical, octahedral, and pyritohedral morphology, respectively. The macroscopic striations, sometimes called triglyphs on cubic crystals, are parallel on specific surfaces and aligned to the <100> directions. Other types of striated and unstriated ( hkl ) surfaces can be observed on pyrite crystals from Peru, a country offering a rich diversity of pyrite shapes. A rare specimen from Elba Island (Italy) is a pyritohedron with uncommon directions of striations (so-called “negative” striations, first described in Japanese minerals). The Wulf kinetic growth and the periodic bond chain (PBC) theories were not relevant enough to explain crystal shapes, the texture of the surfaces, and twinning. To bring some new insights on crystal growth, twinning, and anisotropy, pyrite samples are analyzed using XRD, SEM, and EDS techniques coupled with atomistic simulations. A first analysis points out that sulfur terminations play a key role in the growth of striations in distinguishing the six <001> directions. The negative striated pyritohedral pyrite would be, in fact, a special case that has stabilized the {120} surfaces, which are structurally different from the {210} facets. The {120} surface has a slightly higher surface energy than the {210} surface (surface energies of 1.68 and 1.65 J/m 2 , respectively, calculated with force field methods). {120} pyritohedra from Elba, Italy, are growing next to micaceous iron oxides (a type of hematite), which are also peculiar specimens with magnetic properties. Another specificity is that some rare earth elements have been identified in the pyrite sample from Elba, which leads to a hypothesis that geothermal conditions favor “negative” striations (e.g., discernible in Akita prefecture-Japan, Boyacá-Colombia, and Cassandra-Greece). The striation directions become useful to distinguish ( hkl ) surfaces and to identify twinning as they follow the same patterns on each interpenetrated crystal. The most common twinning is the “iron cross,” a penetration twin of two crystals defined by a rotation of 90° along an [001] axis with a coincidence in the iron sub-lattice (e.g., twinning by merohedry) and with a twin center. The sulfur network also plays a fundamental role in stabilizing the (001) interface and in keeping the chemical bulk properties at the boundary, as confirmed by additional ab initio simulations. The grain boundary is a 2D defect in which the (001) twinning is relatively stable as it is common. The calculated formation energy of the rotation twinning is 0.8 J/m 2 . The rotation twinning is associated with an apparent reflection on (110) planes. The formation energy of the (110) mirror grain boundary is 1.7 J/m 2 , and the interface at the atomic scale is relatively uniform in agreement with experimental observations.

Weathering crusts after granites are the most important source of heavy rare-earth elements (HREE) worldwide. Although HREE in these deposits is known to be inherited from parental rocks, the origin of HREE enrichment and the reasons why it is rare outside of China remains unclear. Here, we report the occurrence of variably organized nanoparticles of Ce-poor (<0.2 wt%), Nd-Y-rich bastnäsite-(La), and associated cerianite in parental granites from a HREE deposit, South China. The mineral contains high-HREE abundances (up to 13 wt% Y 2 O 3 ). Synchrotron radiation-induced X‑ray diffraction and high-resolution transmission electron microscopy analyses suggest that the mineral grew as disordered nanocrystals and (nearly) coaligned nanoparticle aggregations, thus supporting “nonclassical” crystallization mechanisms by particle attachment under hydrothermal conditions. The nanocrystalline Ce-poor, Nd-Y-rich bastnäsite-(La) precipitated at rapidly decreasing temperature related to the influx of externally derived fluids, which caused CO 2 -H 2 O immiscibility and REE supersaturation. This interpretation is supported by petrographic data and microthermometric analysis of fluid inclusions in quartz. Unusually high f O2 resulted in Ce oxidation and decoupling from trivalent lanthanides, producing polycrystalline mineralization.

A new mineral paratobermorite with the ideal crystal-chemical formula Ca 4 (Al 0.5 Si 0.5 ) 2 Si 4 O 16 (OH)·2H 2 O·(Ca·3H 2 O) is a member of the tobermorite group within the tobermorite supergroup. It was found at the Bazhenovskoe chrysotile asbestos deposit, Central Urals, Russia, in cavities of grossular rodingite in association with prehnite, pectolite, thomsonite-Ca, and calcite. Paratobermorite occurs as well-shaped prismatic to acicular crystals up to 1 × 1.5 × 8 mm 3 typically assembled in spray- or bush-like radial clusters or open-work aggregates up to 1.5 cm across, which form interrupted crusts up to 3 × 5 cm 2 . Paratobermorite is transparent, colorless, pale yellowish, pale beige, or pinkish, with a vitreous luster. The mineral is brittle, with the (001) perfect cleavage. The Mohs hardness is ca. 3½. D meas = 2.51 (2) and D calc = 2.533 g/cm 3 . Paratobermorite is optically biaxial (+), α = 1.565 (2), β = 1.566 (2), γ = 1.578 (2), 2 V meas = 25 (10)° and 2 V calc = 32° (589 nm). Optical orientation is: X = c , Y = b , Z = a . The chemical composition of paratobermorite (electron microprobe, H 2 O by selective sorption from gaseous products of heating) is Na 2 O 0.40, K 2 O 0.28, CaO 36.60, MnO 0.04, BaO 0.07, Al 2 O 3 6.46, SiO 2 42.32, H 2 O 14.10, total 100.27 wt%. The empirical formula calculated on the basis of 22 O atoms per formula unit and (O,OH) 17 ·5H 2 O is Na 0.09 K 0.04 Ca 4.72 Al 0.92 Si 5.09 O 15.69 (OH) 1.31 ·5H 2 O. Like other members of the tobermorite supergroup, paratobermorite displays OD character, with two MDO (maximum degree of order) structures: one (MDO1), with non-standard space group F 2/ d 11 and the second (MDO2), just corresponding to the structure-type of the new mineral, with non-standard space group C 1121/ m; its unit-cell parameters obtained from single-crystal X‑ray diffraction data are: a = 11.2220(4), b = 7.3777(2), c = 22.9425(8) Å, γ = 89.990(3)°, V = 1899.46(10) Å 3 , and Z = 4; polytype 2 M . The structure of paratobermorite is solved on a single crystal, R = 8.36%. Like structures of other “tobermorites 11 Å,” it is based on the complex layer built of a sheet of sevenfold Ca-centered polyhedra with wollastonite-type chains of T tetrahedra attached to the Ca-sheet from both sides. The tetrahedral ( T ) sites T 1 and T 2 are fully occupied by Si, while alternating T 3 and T 4 sites are filled by Al and Si in the ratio 1:1. The chains of tetrahedra belonging to neighboring complex layers share common oxygen vertices of the bridging T 3,4 tetrahedra to form xonotlite-type ribbons [Si 6 O 17 ] ∞ . The heteropolyhedral Ca- T -O scaffolding appears as a microporous quasi-framework with wide channels, which contain additional Ca atoms and H 2 O molecules. The complex Ca- T -O layers in paratobermorite (so-called “complex modules of type A”) significantly differ in topology (mutual arrangement of T tetrahedra and Ca polyhedra) from the complex Ca- T -O layers in tobermorite (“complex modules of type B”). IR spectrum confirms the presence of nonequivalent H 2 O molecules and nonequivalent T -O- T angles involving T atoms of two neighboring wollastonite-type chains. Due to the original topological type of the structure and the presence of significant amount of Al, which substitutes Si, paratobermorite can be considered as a novel microporous material, a perspective cation-exchanger.

This study describes the: (1) morphological nature of the calcites in the Toki granite, central Japan; (2) the difference in chemical compositions in terms of morphological classification; and (3) the identification of the stages of calcite formation and the corresponding mass transfer between minerals and fluid owing to hydrothermal alterations and groundwater-rock interactions, which reveals the sequential variations in fluid chemistry during the sub-solidus stage. Calcites in the Toki granite were classified into four types: (1) lenticular calcite in the chloritized biotite; (2) granular calcite in the altered plagioclase; (3) intergranular calcite; and (4) fracture-filling calcite. The lenticular, granular, and intergranular calcites contain greater amounts of iron, manganese, and magnesium than fracture-filling calcites. The lenticular calcite in the chloritized biotite, granular calcite in the altered plagioclase, and intergranular calcite formed due to the precipitation of calcium, iron, manganese, and magnesium released from biotite and plagioclase owing to hydrothermal alterations. The fracture-filling calcites formed at a later stage than the lenticular, granular, and intergranular forms. In the hydrothermal fluid, the concentrations of aluminum, iron, manganese, and magnesium gradually decrease, and the concentration of calcium gradually increases as the alteration proceeds. The chemical characteristics of the fluid at the late stage of hydrothermal alteration and those of the subsequent groundwater are consistent with those of fracture-filling calcites, indicating that the fracture-filling calcites precipitated from the fluid at a late stage of hydrothermal alterations and then from the groundwater. Elements released from biotite and plagioclase owing to hydrothermal alterations were incorporated into and fastened to the calcite. Therefore, the calcites influenced the sequential variations in fluid chemistry during the sub-solidus stage.

Corundum is rarely found in situ within alkali syenites. A corundum-bearing syenite was found in the Yushishan rare metal deposits of the eastern section of the Altyn Tagh fault in the northeastern Tibetan Plateau, but the characteristics and formation of corundum remain unknown. We describe a corundum-bearing syenite dike emplaced in biotite plagioclase gneiss that suffered overprinted deformation with characteristics of mylonitization. The corundum crystals have variable grain sizes, and the largest ones are megacrystic with growth zoning. The corundum crystals contain a variety of mineral inclusions that are divided into primary and secondary. The primary mineral inclusions within the corundum include variable contents of Fe-Ti oxide needles, ilmenite, zircon, monazite-(Ce), potassium feldspar, pyrochlore, columbite-(Fe), magnetite, samarskite-(Y), and pyrite that indicate corundum crystallized in peraluminous Zr-rich and Si-poor alkali rock with variable TiO 2 contents. Secondary mineral inclusions include Zn-rich hercynite, ilmenite, magnetite, annite, fluorapatite, and intergrowths of ilmenite with columbite-(Fe) and goethite that reveal late-stage influx of Zn-, Ti-, Fe-, and F-bearing fluids into corundum that caused metasomatism and element migration and mineral precipitation. The trace element analysis of corundum shows high-Fe and -Ga contents and low-Mg and -Cr contents that are consistent with the characteristics of corundum of magmatic origin. The trace element characteristics and the oxygen isotopes (6.2–8.2‰) results indicate that corundum crystallized in melts with the involvement of Al-rich and Si-poor crustal material.

Light elements alloying with metallic Fe can change the properties and therefore play a key role in the structure and dynamics of planetary cores. Hydrogen and silicon are possible light elements in the rocky planets’ cores. However, hydrogen storage in Fe-Si alloy systems remains unclear at high pressures and high temperatures because of experimental difficulties. Taking advantage of pulsed laser heating combined with high-energy synchrotron X‑ray diffraction, we studied reactions between FeSi and H in laser-heated diamond-anvil cells (LHDACs) up to 61.9 GPa and 3500 K. We found that under H-saturated conditions the amount of H alloying with FeSi (0.3 and < 0.1 wt% for the B20 and B2 structures, respectively) is much smaller than that in pure Fe metal (>1.8 wt%). Our experiments also suggest that H remains in the crystal structure of FeSi alloy when recovered to 1 bar. Further density functional theory (DFT) calculations indicate that the low-H solubility likely results from the highly distorted interstitial sites in the B20 and B2 structures, which are not favorable for H incorporation. The recovery of H in the B20 FeSi crystal structure at ambient conditions could open up possibilities to understand geochemical behaviors of H during core formation in future experiments. The low-H content in FeSi alloys suggests that if a planetary core is Si-rich, Si can limit the ingassing of H into the Fe-rich core.

We identified dmisteinbergite, the rare trigonal polymorph of CaAl 2 Si 2 O 8 , for the first time in high-grade metamorphic rocks. Dmisteinbergite occurs as a crystallization product of silicate melt inclusions (nanogranitoids) in garnet from three host rocks with different protoliths and re-equilibration conditions, i.e., from 1.0 to 4.5 GPa. Raman spectra and compositions of the dmisteinbergite here investigated are overall identical to those of previously characterized artificial and natural dmisteinbergite. In nanogranitoids, this phase coexists with other metastable polymorphs of feldspar (kumdykolite, kokchetavite) and SiO 2 (quartz, cristobalite), recently interpreted as the result of undercooling, supersaturation and rapid crystallization of a silicate melt confined in a micrometric pore. Dmisteinbergite formation likely results from a similar process, and thus it should be regarded as a kinetically controlled phase. Moreover, the investigation of dmisteinbergite as well as of other metastable feldspar polymorphs offers new insights into the behavior of natural materials under non-equilibrium conditions.

This issue of New Mineral Names provides a summary of several new species in the tetrahedrite-group along with examples of how museums are sharing type and cotype specimens. Currently there are approximately 50 sulfosalt mineral species in the tetrahedrite-group that have the general formula M2 ( A 6 ) M1 ( B 4 C 2 ) X3 ( D 4 ) S1 ( Y 12 ) S2 ( Z ), with A = Cu + , Ag + , □; B = Cu + , Ag + ; C = Zn 2+ , Fe 2+ , Hg 2+ , Cd 2+ , Mn 2+ , Ni 2+ , Cu 2+ , Cu + , Fe 3+ ; D = Sb 3+ , As 3+ , Bi 3+ , Te 4+ ; Y = S 2– , Se 2– ; Z = S 2– , Se 2– , □. All members if the tetrahedrite-group are isometric and have potential applications high efficiency thermoelectric materials. Some the type specimens of tetrahedrite, and others in this review, are shared between museums. Having newly described minerals housed at multiple museums provides easier access to specimens for researchers around the world and serves to preserve these minerals in case of loss at any one the institutions. Here we look at the descriptions of stibiogoldfieldite, graulichite-(La), tennantite-(Cu), wildcatite, ellinaite, paqueite, burnettite, saccoite, and gurzhiite.