Volume 100, Issue 1

Nanominerals are characterized by crystal dimensions that fall between 100 and 1 nm, and as the length scale of atomic ordering approaches the lower end of this range, a material’s physical and chemical properties may dramatically diverge from what is observed at the macroscale. Indeed, when atomic correlation lengths approximate the dimensions of the unitcell, one can reasonably ask whether a natural material should be classified as a mineral at all. In their Outlook contribution, Caraballo et al. (2014) offer a state-ofthe- art assessment of the science of environmental nanominerals, with an emphasis on the role that crystallinity plays in their behavior.

The field of mineral evolution-a merger of mineralogy and Earth history-coalesced in 2008 with the first of several global syntheses by Robert Hazen and coworkers in the American Mineralogist. They showed that the cumulative abundance of mineral species has a stepwise trend with first appearances tied to various transitions in Earth history such as the end of planetary accretion at ca. 4.55 Ga and the onset of bio-mediated mineralogy at ca. >2.5 Ga. A global age distribution is best established for zircon. Observed abundance of zircon fluctuates through more than an order of magnitude during successive supercontinent cycles. The pulse of the Earth is also recorded, albeit imperfectly, by the 87Sr/86Sr composition of marine biogenic calcite; the Sr-isotopic ratio of this mineral reflects the balance of inputs of primitive strontium at midocean ridges and evolved strontium that drains off the continents. A global mineral evolution database, currently in the works, will greatly facilitate the compilation and analysis of extant data and the expansion of research in mineralogy outside its traditional bounds and into more interdisciplinary realms.

Subduction generated a NW-trending Andean arc along the Californian margin beginning at ~175 Ma. Coeval high-pressure (HP) transformation of oceanic crust in an east-dipping, subduction zone probably accompanied plate convergence, but recovered Franciscan eclogite and garnet blueschist blocks chiefly possess younger recrystallization ages of ~165-150 Ma. These Jurassic HP metamafic rocks were sequestered in a low-temperature environment well into Cretaceous time. Fragments of actinolitic rinds partially surround many such high-grade blocks. Only slightly younger than the HP metamorphism, these rinds reflect metasomatic exchange between metabasalt and serpentinized harzburgite along the dynamic oceanic crust-mantle hanging wall during storage of the mafic rocks at moderate depth. High-grade tectonic blocks later were brought toward the surface in circulating, low-density, sheared mud-matrix mélange and/or in buoyant serpentinite bodies. Most exotic HP metamafic blocks occur in mélanges of the Franciscan Central Belt, reflecting tectonic insertion within the subduction zone-not near-surface additions to the clastic section. However, rare, high-grade clasts in feebly recrystallized Franciscan conglomerates suggest erosion and sedimentary deposition for some HP blocks. The addition of dense metabasaltic olistoliths to the mid- and Upper Cretaceous section requires that these HP material were carried surfaceward first as tectonic fragments, perhaps immersed in low-density serpentinite or mud-matrix mélange, then eroded and transported into the trench. HP rocks are conspicuously lacking in coeval Great Valley strata. Whatever the origin of particular high-grade rocks, widespread post-depositional shearing has largely obliterated their original natures, but all dense metamafic blocks of Jurassic recrystallization age must have been supplied to the Cretaceous Franciscan accretionary complex by entrainment in a low-density, circulating muddy matrix or serpentinite body. The vast majority of exotic HP blocks resides in Central Belt mélanges, and appears to be tectonic rather than olistostromal in origin.

Environmental mineralogy is rapidly expanding in technological directions that allow for the detection, characterization, and understanding of non-crystalline and poorly crystalline phases, crystalline-amorphous mixed phases, and nanosized naturally occurring materials. Specifically, this article provides a perspective view of the broad range of structural complexity/heterogeneity observed in environmental minerals and amorphous materials, as well as our current understanding of how these materials can be best observed, evaluated, and described, and why this is important in the mineralogical sciences. The discussion is broken down into the assessment of short- and medium-range order in amorphous materials, and the nature of nanominerals and mineral nanoparticles, amorphousnanocrystalline transitional phases, and mesocrystals. These materials do not fit one or more aspects of the most commonly used definitions of a mineral (although some of them are formally recognized as minerals, such as ferrihydrite and schwertmannite), yet they do fit other portions of these current definitions. Nevertheless, because these phases can be exceptionally minute in size, and/or not highly crystalline, and/or generally much less abundant than other mineral components in the system, they may be underappreciated and/or understudied, or, apparently as is often the case, completely missed. Yet they are often highly relevant to, and in many cases dominant in, important aspects of how the (bio)geochemistry of an environmental system operates. Furthermore, although it is important to analytically and experimentally characterize synthetic equivalent phases in the laboratory, often under conditions intended to mimic one or a few aspects of the real environment, we argue that it is imperative to study natural, intact (as much as possible) samples and make field measurements with much greater frequency than is currently practiced.

Impurities and crystal defects within the semiconducting bulk of a metal sulfide introduce energy levels within the forbidden bandgap. These levels in turn control semiconducting type and local electrical properties within single and multi-phased sulfide assemblages. Heterogeneity in sulfide semiconductivity linked to these impurities can lead to p-n micro-junction formation and potential distributions near the surface that may alter redox reactivity. Secondary gold ore genesis via a micro-galvanic effect related to heterogeneity has in the past been hypothetically linked to such micro-junctions. Understanding these regions and their interaction with weathering fluids in the regolith for example requires large-scale imaging of potential distributions associated with near-surface micro-junctions and correlation with the responsible elemental distributions. Here we investigate the existence of micro-electronic junctions in a mixed sulfide assemblage using scanning laser beam induced current (LBIC) and correlate them with pyrite-chalcopyrite interfaces mapped using combined energy-dispersive spectroscopy (EDS) and wavelength-dispersive spectroscopy (WDS) on an electron hyper-probe. Junctions in a natural assemblage are positively identified for the first time.

The structure of water-saturated Ca- and Mg-bearing carbonate melts under reducing and oxidizing conditions was investigated in a series of hydrothermal anvil cell experiments conducted at 400-1100 °C and 442-2839 MPa. Equilibria were investigated in the calcite-H 2 O, calcite-CaO-H 2 O, magnesite- H 2 O, and magnesite-MgO-H 2 O systems, with redox conditions controlled by Re/ReO 2 and Ti/TiO 2 assemblages. Melting relationships and the C-O-H speciation of the coexisting aqueous fluid and melt were assessed in situ by Raman vibrational spectroscopy. Hydrous melting of MgCO 3 -MgO occurred at ~850 °C, 1.5-2 GPa. In the CaCO 3 -CaO-H 2 O system, melt was formed at 600-900 °C and pressures of 0.5-1.5 GPa because of melting-point depression imposed by the presence of CaO. The C-O-H speciation of the carbonate melts and coexisting supercritical aqueous solutions was mainly H 2 O and CO 3 2- , with traces of CO 2 (aq) and CH 4 (aq) in the fluid phase. The melt-fluid H 2 O partition coefficients attained in the Mg-bearing melt (median 0.5) were higher than in the Ca-bearing melt (median 0.3). Under oxidizing redox conditions, dissolved ReO 2 - was present in all phases, underscoring the enhanced solubility of metals in carbonate-bearing melts and carbonatites. In effect, the enhanced solubility of H 2 O along with the ionic nature of the carbonate melts may promote the solvation of ionic species in the melt structure. From in situ vibrational spectroscopy, the v 1 -CO 3 2- vibration recorded in the melt spectra suggests the presence of intermolecular interactions between the oxygen of the carbonate ion with water dissolved in the melt. The thermodynamic properties of this water appear to be similar to the supercritical aqueous phase. For example, the estimated enthalpy for the breakage of the hydrogen bonding between water molecules attained values of 6.8 ± 1.5 kcal/mol and 8.4 ± 1.3 kcal/mol in the melt and fluid phase, respectively. The calculated partial molar volume of H 2 O in the melt (~48 ± 6 cm 3 /mol) is also comparable to the partial molar volume of supercritical water at similar conditions. Interestingly, this value is considerably greater than published partial molar volume values for H 2 O in silicate melts (10-12 cm 3 /mol). The pressure-temperature melting relationships of the CaO-CO 2 -H 2 O and MgO-CO 2 -H 2 O systems highlight the important role of water and alkaline earth oxides on the hydrous melting of the carbonatebearing subducting oceanic crust. Carbonates present in marine sediments or serpentinized peridotites may melt before complete dehydration at the slab-mantle wedge transition zone, and thus, never reach sub-arc depths. To this end, melting of carbonate minerals at crustal temperatures and pressure can contribute to the volcanic CO 2 flux at the arc through melt/fluid interactions.

The effect of pressure and temperature on the structure of silicate melts coexisting with silicasaturated aqueous electrolyte fluids enriched in fluorine or chlorine in the Na 2 O-Al 2 O 3 -SiO 2 -H 2 O system has been described. In situ measurements were conducted with the samples at desired temperatures and pressures in a hydrothermal diamond-anvil cell (HDAC) by using microRaman and FTIR spectroscopy techniques. The data were acquired at temperatures and pressures up to 800 °C and 1264 MPa, respectively. In silicate melts, the intensity of the infrared bands assigned to the stretch vibration of OH-groups is smaller than those of coexisting molecular H 2 O when F and Cl are present in the melt structure. This difference reflects the interaction of F or Cl with H 2 O in the melts. With decreasing pressure and temperature (P-T) conditions, SiF complexes are favored in the melt over that in coexisting fluid, perhaps because of decreasing silicate concentration in fluids with decreasing temperature and pressure. In these melts, the solubility of Cl, likely in the form of NaCl, increases with decreasing P-T conditions, whereas the abundance of such complexes in coexisting fluids decreases in favor of HCl. Our experimental data were employed to model the ascent of a fluid-saturated magma from the upper mantle to the shallow crust. This modeling offers insights into F and Cl partitioning between and the speciation of F and Cl in melts and magmatic fluids. We suggest that the formation of stable SiF and NaCl complexes and their increasing solubilities in silicate melts during magma ascent may explain the late volcanic degassing of F and Cl compared with the degassing behavior of other volatile species.

We determined phase relations in MgCr 2 O 4 at 12-28 GPa and 1000-1600 °C using a multi-anvil apparatus. At 12-15 GPa, spinel-type MgCr 2 O 4 (magnesiochromite) first decomposes into a mixture of new Mg 2 Cr 2 O 5 phase + corundum-type Cr 2 O 3 at 1100-1600 °C, but it dissociates first into MgO periclase + corundum-type Cr 2 O 3 at l000 °C. At about 17-19 GPa, the mixture of Mg 2 Cr 2 O 5 phase + corundum-type Cr 2 O 3 transforms to a single MgCr 2 O 4 phase. Structure refinements using synchrotron X-ray powder diffraction data indicated that the high-pressure MgCr 2 O 4 phase has a CaTi 2 O 4 -type structure (Cmcm), and that the basic structure of the Mg 2 Cr 2 O 5 phase is the same as that of recently found modified ludwigite-type Mg 2 Al 2 O 5 and Fe 2 Cr 2 O 5 (Pbam). The phase relations in this study may suggest that natural chromitites in the Luobusa ophiolite regarded as the deep-mantle origin were derived from the mantle shallower than the depths corresponding to pressure of 12-15 GPa because of absence of the assemblage of (Mg,Fe) 2 Cr 2 O 5 + Cr 2 O 3 in the chromitites.

Sulfate minerals are important indicators for aqueous geochemical environments. The geology and mineralogy of Mars have been studied through the use of various remote-sensing techniques, including thermal (mid-infrared) emission and visible/near-infrared reflectance spectroscopies. Spectral analyses of spacecraft data (from orbital and landed missions) using these techniques have indicated the presence of sulfate minerals on Mars, including Fe-rich sulfates on the iron-rich planet. Each individual Fe-sulfate mineral can be used to constrain bulk chemistry and lends more information about the specific formational environment [e.g., Fe 2+ sulfates are typically more water soluble than Fe 3+ sulfates and their presence would imply a water-limited (and lower Eh) environment; Fe 3+ sulfates form over a range of hydration levels and indicate further oxidation (biological or abiological) and increased acidification]. To enable better interpretation of past and future terrestrial or planetary data sets, with respect to the Fe-sulfates, we present a comprehensive collection of mid-infrared thermal emission (2000 to 220 cm -1 ; 5-45 μm) and visible/near-infrared (0.35-5 μm) spectra of 21 different ferrous- and ferric-iron sulfate minerals. Mid-infrared vibrational modes (for SO 4 , OH, H 2 O) are assigned to each thermal emissivity spectrum, and the electronic excitation and transfer bands and vibrational OH, H 2 O, and SO 4 overtone and combination bands are assigned to the visible/near-infrared reflectance spectra. Presentation and characterization of these Fe-sulfate thermal emission and visible/near-infrared reflectance spectra will enable the specific chemical environments to be determined when individual Fe-sulfate minerals are identified.

Trace element, Hf, and O isotopic composition and U-Pb geochronological data are reported for zircon megacrysts found in miaskitic (zircon, biotite, plagioclase-bearing) nepheline syenite pegmatites from the Finero complex in the Northeastern part of the Ivrea-Verbano Zone, southern Alps. Zircon from these pegmatites was reported to reach up to 9 cm in length and is characterized by ~100 μm spaced planar fractures in different directions. Small volumes of these highly evolved alkaline melts intruded into the lower crust and were emplaced within amphibole peridotites and gabbros between 212.5 and 190 Ma. A zircon crystal of 1.5 cm size records a systematic core-to-rim younging of 4.5 Ma found by high-precision CA-ID-TIMS 206 Pb/ 238 U dating of fragments, and of 8.7 Ma detected by laser ablation ICP-MS spot dating. Volume diffusion at high temperatures was found to be insufficient to explain the observed within-grain scatter in dates, despite the fact that the planar fractures would act as fast diffusion pathways and thus reduce effective diffusion radii to 50 μm. The U-Pb system of zircon is therefore interpreted to reflect an episodic protracted growth history. These high-pressure miaskites probably formed by episodic, low-degree decompression melting of a metasomatically enriched mantle source and subsequent crystallization in the lower crust at volatile saturation with explosive volatile release, evidenced by their brecciated texture in the field and by the occurrence of planar fractures in zircon. They point to the existence of a long-lived period of heat advection in the deep crust by highly differentiated melts from enriched, lithospheric mantle.

The Berry-Havey pegmatite (Oxford pegmatite field, Androscoggin County, Maine, U.S.A.), enriched in Li, F, B, Be, and P, is intruded in hornblende-rich amphibolite, with minor biotite or diopside. The pegmatite has a complex internal structure, with four texturally and compositionally different zones that show an increasing degree of evolution inward: wall zone, intermediate zone, core margin, and core zone. The main minerals are quartz, feldspars, Al-micas, tourmaline, with minor Fe-micas, garnet, beryl, amblygonite-montebrasite, Fe-Mn phosphates, and apatite. Tourmaline is present in all zones of the pegmatite, showing different textures: black anhedral crystals in the wall and intermediate zones; black prisms of up to 40 cm in length in the intermediate zone; black tapered prisms, surrounded by a pseudo-graphic intergrowth of quartz or albite with black ± green/bluish tourmaline, and constituting a continuous layer under the core zone; multicolored and “watermelon” zoned crystals in the core zone; and gemmy deep green and color-zoned “watermelon” tourmaline prisms, up to 15 cm length, inside the pockets. A complete chemical evolution from Mg-rich schorl in the wall zone to elbaite with an important deprotonation in the pockets inside the core zone is observed. The most plausible exchange vectors for this chemical evolution are FeMg -1 , Y Al W O[ Y R 2+W (OH)] -1 and Al[X] X (R 2+ Na) -1 (where R 2+ = Fe 2+ +Mg 2+ +Mn 2+ +Zn 2+ ), for the tourmalines from the wall and intermediate zones. In the core margin, tourmaline composition evolves from schorl toward Li-rich species through the substitution ( Y Al Y Li Y R 2+ -2 ). Later, during the crystallization of the core zone, this exchange vector combined with the substitution ([X] Y Al 0.5 X Na -1 Y Li -0.5 ). Finally, the gemmy tourmalines from the pockets show a deprotonation related to the exchange vector Y Al W O 2 Y Li -1 W (OH) -2 and may be classified as darrellhenryite. These substitutions may reflect an increase in oxygen fugacity and a decrease in Li and F related to the crystallization of lepidolite and amblygonite-montebrasite in the core zone adjacent to or within the pockets. The crystallization of these minerals would reduce the availability of Li and F for the very latest tourmaline crystals, growing inside the pockets, where the deprotonation becomes important. Chemical and textural variation in tourmaline is consistent with a fractional crystallization process for the internal evolution of the Berry-Havey pegmatite. Crystallization of the tourmaline layer under the core zone may be related to the exsolution of the fluid phase implied in the formation of pockets.

The crystal structure of alumohydrocalcite was determined using synchrotron X-ray radiation. Alumohydrocalcite crystallizes in the triclinic P1̅ space group with unit-cell parameters: a = 5.71(5), b = 6.54(4), c = 14.6 (2) Å, α = 81.8(3)°, β = 83.9(3)°, γ = 86.5(7)°, and V = 537(7) Å 3 . This mineral has the formula CaAl 2 (CO 3 ) 2 (OH) 4 ·4H 2 O as opposed to the commonly accepted formula CaAl 2 (CO 3 ) 2 (OH) 4 ·3H 2 O. The fourth water molecule interacts with the strongly bonded polyhedral unit of the structure through hydrogen bonds and connects three adjacent units. This water molecule plays a major role in crystal stability. On heating the sample, this fourth water molecule escapes from the crystal structure as a first one at lower temperature (~105 °C) than the other water molecules in the crystal structure (~128 °C). Analysis and description of the alumohydrocalcite crystal structure and particularly of the intermolecular interactions, together with a comparison to the crystal structures of other minerals with the analog formula M 2+ M 3+ 2 (CO 3 ) 2 (OH) 4 ·nH 2 O, suggests that this mineral is an extension of the dundasite group that should, we propose, be formed for all minerals with the above formula (dundasite, dresserite, strontiodresserite, petterdite, kochsándorite, hydrodresserite, and alumohydrocalcite). They all exhibit very similar patterns on Hirshfeld surfaces. Hirshfeld surfaces appear to be a very useful tool in the analysis of interactions, classification, and validation of mineral crystal structures.

Dense, high-refractive index, ultra-hard, wide-gap polymorphs of SiO 2 , recently discovered orthorhombic seifertite (space group 60 Pbcn), and earlier characterized tetragonal stishovite (space group 136 P42/mnm) and monoclinic coesite (space group 15 C2/c) were studied using advanced methods of electronic structure calculations involving full-potential linearized augmented plane wave density functional theoretical method (FP-LAPW-DFT) with spin polarization, orbital-dependent potentials, and modified Becke-Johnson potential (mBJ) for accurate account of the band gaps. Although these calculations yield an excellent account of many properties, we here focus on quantitative aspects of optical absorption and selection rules therein. Specifically, the valence-to-conduction band transition in seifertite is symmetry-allowed, and is symmetry-forbidden in stishovite and coesite. Theory is compared with published experimental data, and explanation is provided for weak pre-edge optical absorption in stishovite. Electronic structure and calculated properties of stishovite are also compared with those of the isostructural rutile TiO 2 . Effective masses are calculated from the energy dispersion curves E(k) at the valence band maximum for holes and conduction band minimum for electrons. In addition, we propose that splitting of the O2p valence-band in coesite and also observed in α-quartz is a general feature of polymorphs with tetrahedrally coordinated Si, in contrast with continuous valence bands in those with octahedral SiO 6 units such as seifertite and stishovite. Based on quantitative results obtained from the BVA theory, this difference originates from a high degree of covalence in the tetrahedral polymorphs as opposed to high iconicity in octahedral polymorphs.

The phase relations in the Na 2 CO 3 -(Fe 0.87 Mn 0.06 Mg 0.07 )CO 3 system have been studied in Kawai-type multi-anvil experiments using graphite capsules at 6.0 GPa and 900-1400 °C. Subsolidus assemblages comprise the stability fields of Na 2 CO 3 + Na 2 Fe(CO 3 )2 and Na 2 Fe(CO 3 ) 2 + siderite with the transition boundary at X(Na 2 CO 3 ) = 50 mol%. Intermediate Na 2 Fe(CO 3 ) 2 compound has rhombohedral R3̅ eitelite structure with cell parameters a = 4.9712(16), c = 16.569(4) Å, V = 354.61(22). The Na 2 CO 3- Na 2 Fe(CO 3 ) 2 eutectic is established at 1000 °C and 66 mol% Na 2 CO 3 . Na 2 Fe(CO 3 ) 2 disappears between 1000 and 1100 °C via incongruent melting to siderite and a liquid containing about 55 mol% Na 2 CO 3 . Siderite remains a subliquidus phase at 1400 °C at X(Na 2 CO 3 ) ≤ 30 mol%. The ternary Na 2 CO 3 -FeCO 3 -MgCO 3 system can be built up from the corresponding binary systems: two systems with intermediate Na 2 (Mg,Fe)(CO 3 ) 2 phase, which melts congruently at the Mg-rich side and incongruently at the Fe-rich side, and the (Mg,Fe)CO 3 system with complete solid solution. The phase relations suggest that the maximum contribution of FeCO 3 component into the lowering solidus temperatures of Na-bearing carbonated mantle domains could not exceed several tens of degrees Celsius.

Chlorine-hydroxyl diffusion was measured in pargasitic amphibole from Yunnan province, China at 1.0 GPa, 625 to 800 °C. Experiments were performed by immersing unoriented crystals in waterbearing NaCl in a piston cylinder for durations from 100 to 454 h. Diffusion profiles were on the order of greater than tens of micrometers in length, and electron microprobe analysis allow us to extract semi-quantitative diffusivities from these experiments. The preliminary diffusion coefficients for chlorine in amphibole in the water-bearing experiments are 2.6 × 10 -16 m 2 /s at 625 °C, 4.9 × 10 -16 m 2 /s at 650 °C, 7.6 × 10 -16 m 2 /s at 700 °C, 1.8 × 10 -15 m 2 /s at 750 °C, 2.8 × 10 -15 m 2 /s at 800 °C. For temperatures between 625 and 800 °C, the Arrhenius relation for chlorine-hydroxyl diffusion has an activation energy of 106.6 ± 7.8 kJ/K mol and a D 0 of 4.53 (+7.3, -2.8) × 10 -10 m 2 /s. Our measurements do not show evidence of anisotropy in the diffusion of Cl-OH into amphibole, but future experiments need to better investigate this possibility.

The bond-valence model has, for several decades, been widely used for creating quantitative structure-activity relationships (QSARs), crystal structure modeling, and verification of proposed structures. Certain limitations of the model, such as the neglect of interactions between cations and between anions, have prevented it from being more broadly applied. In this work, we use cation-cation and anion-anion bonds to augment the existing bonding model in the systems H-Al-Si-O and K-Al-Si- O. The bond valence-length curves for these interactions employ the same mathematical form as ionic bonds, but make only a small contribution to the overall bonding in ionic materials. In the systems examined here, oxygen-oxygen interactions were much more important than those between cations for producing accurate bond-valence sums. Both anion-anion and cation-cation bonding could prove important, however, for our ultimate goal of producing valence-based force fields for use in molecular dynamics simulations. Rolling these interactions into the bond-valence framework would produce behavior similar to hard-sphere repulsive or van der Waals terms, but would more flexibly account for the complete bonding environment. The overall improvement in valence sums was robust, was maintained outside the calibration set, and was invariant to elemental substitution. We conclude that this minor alteration of the bond-valence approach will significantly improve bond-valence models in conjunction with other recent extensions of the approach.

The bond-valence model (BVM) posits an inverse relationship between bond valence (essentially bond order) and bond length, typically described by either exponential or power-law equations. To assess the value of these forms for describing a wider range of bond lengths than found in crystals, we first assume that the bond critical point density (ρ b , reported in e - /Å 3 ) is at least roughly proportional to bond valence. We then calculate ρ b -distance curves for several diatomic pairs using electronic structure calculations (CCSD/aug-cc-pVQZ) and Atoms-In-Molecules (AIM) analysis. The shapes of these curves cannot be completely described by the standard exponential and power-law forms, but are well described by a threeparameter hybrid of the exponential and power-law forms. The ρ b -distance curves for covalent bonds tend to exhibit exponential behavior, while metallic bonds exhibit power-law behavior, and ionic bonds tend to exhibit a combination of the two. We next use a suite of both experimental and calculated (B3LYP/ Def2-TZVP) molecular structures of oxo-molecules, for which we could infer X-O bond valences of ~1 or ~2 v.u., combined with some crystal structure data, to estimate the curvature of the bond valencelength relationship in the high-valence region. Consistent with the results for the ρ b -distance curves, the standard forms of the bond valence-length equation become inadequate to describe high-valence bonds as they become more ionic. However, some of these systems demonstrate even higher curvature changes than our three-parameter hybrid form can manage. Therefore, we introduce a four-parameter hybrid form, and discuss possible reasons for the severe curvature. Although the addition of more parameters to the bond valence-length equation comes at a cost in terms of model simplicity and ease of optimization, they will be necessary to make the BVM useful for molecular systems and transition states.

By using atomistic simulation and configurational statistics techniques, the thermodynamics of mixing for calcite-smithsonite solid solutions have been investigated. By employing a 2 × 2 × 1 supercell, the configuration with the lowest energy for the solid solution with a certain composition was determined. The incorporated Zn 2+ tends to occur at the sites neighboring to another substituted Zn 2+ within the (0001) layer, but the substituted layers are preferentially segregated by calcite layers, and vice versa. The supercells with compositions around the two end-members stand positive enthalpies at any temperatures, whereas those supercells with composition of about Ca 0.5 Zn 0.5 CO 3 prominently exhibit negative values in various temperatures of reality (e.g., <1000 K). The free energies are prominently negative at high temperatures (>1500 K) for the whole range of compositions, only those around both end-members have positive values at some low temperatures (<1200 K). In the derived phase relations of this solid solution system, the potential incorporation content of ZnCO 3 into calcite is only 0-2.5% mole fraction (i.e., Zn content of 0-1.6 wt%) in most geochemistry equilibrium processes, and vice versa.

Subduction of rocks into the mantle results in high-pressure metamorphism and the formation of eclogites from basaltic precursor rocks. In general, many kilometers of oceanic lithosphere are ultimately consumed prior to the subsequent continental slab subduction and collision. The exposure of the eclogites derived from oceanic subduction and continental subduction at the surface of Earth today record provide different P-T-t records of the subduction process. The Huwan shear zone in the Hong’an orogenic belt, marking a former ocean-continent transition zone, has been the focus of many studies on subduction-related high-pressure metamorphism. In this study, Lu-Hf garnet, U-Pb zircon, and Ar- Ar mica ages are combined with geochemical data to understand the origin of two coexisting eclogite bodies exposed along the Xuehe River in the Huwan Shear zone. In total, the results indicate that the two eclogites have different protoliths but experienced a similar metamorphic history. This observation requires new tectonic model for the coupled subduction of oceanic and continental crust in subduction zones. Combined geochemistry and zircon U-Pb geochronology suggest distinct oceanic and continental affinities for the eclogite protoliths. The Lu-Hf dates of 261.5 ± 2.4 Ma of the continental-type eclogite and 262.7 ± 1.7 Ma of the oceanic-type eclogite reflect garnet growth and are interpreted to closely approximate the age of eclogite-facies metamorphism. Therefore, both the geochemically oceanic- and continental-type eclogites underwent the same episode of Permian eclogite-facies metamorphism. The Permian Lu-Hf ages of ca. 262 Ma and the obtained Triassic Ar-Ar ages (~240 Ma) of the oceanic-type and continental-type eclogites imply coupled subduction and exhumation of oceanic and continental crustal materials in the Hong’an orogenic belt during the Permian and the Triassic. Though limited, the geochemical and geochronological results of this study, together with the discrepant Carboniferous dates for the nearby eclogites of previous studies, apparently suggest that the Huwan shear zone was not always a single coherent unit but instead comprises different tectonic slices that were metamorphosed at different times before final assembly. Some slices of the oceanic and continental crust underwent two subduction cycles during the Carboniferous and the Permian, whereas some eclogites registered only a single subduction-exhumation loop during the convergence between the South China Block and the North China Block in the Huwan shear zone. The consistent ages of the oceanic- and continental-type eclogites disfavor the traditional mélange model that high-pressure rocks are dismembered fragments that have been assembled and intercalated with rocks devoid of any high-pressure history at shallow crustal levels, forming a tectonic mélange.

Sepiolite is an industrially important clay mineral of the palygorskite-sepiolite group with alternating 2:1 ribbons and hydrated tunnels. Dry sepiolite, Mg 8 Si 12 O 30 (OH) 4 (OH 2 ) 4 , loses half of its OH 2 content upon further heating and undergoes a structural collapse known as folding. This treatment is considered essential for enhancing the absorptive properties of the clay. In this paper, the folding process is studied by near-infrared (NIR) spectroscopy, mid-infrared attenuated total reflectance (ATR), and thermogravimetric analysis (TGA). The folded state, Mg 8 Si 12 O 30 (OH) 4 (OH 2 ) 2 , reveals a new spectrum of fundamental and higher-order OH 2 vibrations, as well as systematically split doublets of structural and surface O-H vibrations. Detailed assignments for the stretching, combination, and overtone O-H modes are proposed on the basis of the two non-degenerate populations of Mg 3 OH (and SiOH) present in the folded state. It is demonstrated that NIR is of particular diagnostic value in monitoring conveniently and non-invasively the folding process, which appears as a simple transition between well-defined dry- and folded-structures. At the level of elementary sepiolite particles (laths), folding is described as a cooperative process requiring the integrity of the ribbons and the inter-ribbon linkages (moderately acid-leached sepiolite does not fold). This is opposed to the skewed and sometimes complex OH2 desorption trace observed by high-resolution TGA, which appears to indicate a multimodal distribution of laths. It is proposed that the rate-determining step for a sepiolite (also, palygorskite) lath to fold is the creation of a critical zone at mid-particle length, which is OH 2 -deficient and contains unstable, fivefold-coordinated Mg 2+ .

The sulfides are an important group of minerals. As a geochemical tracer, the sulfur isotope fractionation in sulfides can be used to analyze the ore-forming process and the ore-forming material source. Fe, Co, Ni, and Mn are the first row transition metals, and pyrite (FeS 2 ), cattierite (CoS 2 ), vaesite (NiS 2 ), and hauerite (MnS 2 ) crystallize in the pyrite-type structure. However, there are few studies on the sulfur isotope fractionation in these disulfides. So studying the isotope fractionation between them provides the opportunity to examine the various members of a structural group in which only the metal atom is changed, thereby providing information that permits a systematic development of concepts regarding sulfur isotope fractionation in transition-metal disulfides. In the present paper, the sulfur isotope fractionation parameters for pyrite, cattierite, vaesite, and hauerite with the pyrite-type structure have been calculated using first-principles methods based on density functional theory in the temperature range of 0-1000 °C. The structure parameters of these four minerals and the vibration frequencies of pyrite are in good agreement with previous experimental values. The metal-sulfur distance increases in the order FeS 2 , CoS 2 , NiS 2 , and MnS 2 , the sulfur-sulfur distance decreases in the order FeS 2 , CoS 2 , MnS 2 , and NiS 2 , these two sequences agree with the experimental results. Our calculations show that the order of heavy isotope enrichment is pyrite > cattierite > vaesite > hauerite. It seems that the sulfur isotope fractionation in disulfides depends mainly on the metal-sulfur bonds.

Tetrataenite is an equiatomic and highly ordered, non-cubic Fe-Ni alloy mineral that forms in meteorites from the distortion of fcc taenite due to extremely slow cooling. The mineral has drawn much attention of the scientific community because of its superb magnetic properties, which may make the phase an alternative to the REE-based permanent magnets. Barring only a few passing mentions, the mineral has never been described from any terrestrial rock. Here we report the characteristics of terrestrial tetrataenite from an ophiolite-hosted Ni-bearing magnetite body from the Indo-Myanmar ranges, northeast India. Although the mineral assemblage surrounding it is very similar to that found in the meteorites, the postulated cooling regimes cannot be similar. The mineral is formed as a consequence of hydrothermal alteration of ferromagnesian minerals of the olivine and pyroxene groups. Iron and nickel were released from the silicates and precipitated in the form of Fe-Ni alloy at low temperature in extremely reducing conditions with a lack of sulfur. Our findings suggest a low-temperature hydrothermal origin of tetrataenite warrants a re-examination of the Fe-Ni phase diagram at low temperatures and puts a question mark on the age-old concept of tetrataenite formation as due solely to extremely slow cooling of fcc taenite in meteorites. It also opens up a new vista for adoption of a hydrothermal route to synthesize this rare material.

Unit-cell parameters of a series of synthetic garnets with the pyrope, grossular, and four intermediate compositions were measured up to about 900 K and to 10 GPa using synchrotron X-ray powder diffraction. Coefficients of thermal expansion of pyrope-grossular garnets are in the range 2.10-2.74 × 10 -5 K -1 and uniformly increase with temperature. Values for the two end-members pyrope and grossular are identical within experimental error 2.74 ± 0.05 × 10 -5 K -1 and 2.73 ± 0.01 × 10 -5 K -1 , respectively. Coefficients of thermal expansion for intermediate compositions are smaller than those of end-members and are not linearly dependent on composition. Bulk modulus of grossular is Κ 0 = 164.3(1) GPa (with Κ 0 ′ the pressure derivative of the bulk modulus fixed to 5.92) and bulk modulus of pyrope is Κ 0 = 169.2(2) GPa (with Κ 0 ′ fixed to 4.4) using a third-order Birch-Murnaghan equation of state, which are consistent with previously reported values. The bulk moduli of garnets of intermediate composition are between ~155 and ~160 GPa, smaller than those of the end-members no matter which Κ 0 ′ is chosen. The compositional dependence of bulk modulus resembles the compositional dependence of thermal expansion. Intermediate garnets on this binary have large positive excess volume, which makes them more compressible. We find that excess volumes in the pyrope-grossular series remain relatively large even at high pressure (~6 GPa) and temperature (~800 K), supporting the observation of crystal exsolution on this garnet join. The curiously “W”-shaped compositional variation of thermal expansion and bulk modulus is anti-correlated with the compositional dependence of microstrain documented in our companion paper (Du et al. in preparation) on the excess volumes in this series of garnets. Minimum thermal expansions and bulk moduli go with maximum microstrains.

Phase relations in the system K 2 CO 3 -CaCO 3 have been studied in the compositional range, X(K 2 CO 3 ), from 100 to 10 mol%, at 6.0 GPa and 900-1450 °C. At 900-950 °C, the system has three intermediate compounds: K 6 Ca 2 (CO 3 ) 5 , K 2 Ca(CO 3 ) 2 , and K 2 Ca 3 (CO 3 ) 4 . The K 2 Ca(CO 3 ) 2 compound decomposes to the K 6 Ca 2 (CO 3 ) 5 + K 2 Ca 3 (CO 3 ) 4 assembly above 950 °C. The K6Ca2(CO 3 ) 5 and K 2 Ca 3 (CO 3 ) 4 compounds melt congruently slightly above 1200 and 1300 °C, respectively. The eutectics were established at 64 and 44 mol% near 1200 °C and at 23 mol% near 1300 °C. K 2 CO 3 remains as a liquidus phase at 1300 °C and 75 mol% and melts at 1425 ± 20 °C. Aragonite remains as a liquidus phase at 1300 °C and 20 mol% and at 1400 °C and 10 mol%. CaCO 3 solubility in K 2 CO 3 and K 2 CO 3 solubility in aragonite are below the detection limit (<0.5 mol%). Infiltration of subduction-derived K-rich Ca-Mg-Fe-carbonatite into the Fe 0 -saturated mantle causes the extraction of (Mg,Fe)CO 3 components from the melt, which shifts its composition toward K-Ca-carbonatite. According to our data this melt can be stable at the P-T conditions of subcratonic lithosphere with geothermal gradient of 40 mW/m 2 corresponding to temperature of 1200 °C at 6 GPa.

Partition coefficients ( Min/L D) for a series of geochemically relevant elements have been calculated from combined EMP/LA-ICP-HRMS analyses of plagioclase, alkali feldspar, Ti-magnetite, biotite, apatite, and trachytic/trachyphonolitic melt pairs in selected Campi Flegrei rocks. Pl/L D and Kfs/L D values are generally very low for most of the trace-elements but Sr, Ba, and Eu. Kfs/L D for the latter elements record a systematic increase as the melt composition changes from trachyte to trachyphonolite, likely due to increasing structural compliance of the sanidine in the trachyphonolites related to larger Na/K values. Conversely, Kfs/L D values for transitional, highly charged incompatible elements (e.g., LREE) decrease from trachyte to trachyphonolite, possibly in response to the decrease of melt polymerization. Min/L D values for titanomagnetite generally decrease with the increasing melt evolution, the highest values being those measured for Ti, V, and Sc. Ti, Ba, Sc, Rb, Nb, Ta, and V are compatible in biotite in equilibrium with trachytic melt, whereas Cs, Sr, and Pb are incompatible and REE are strongly incompatible, as supported by the extremely low Bt/L D Y (0.003-0.008). Partition coefficients for apatite and trachyphonolitic glass pairs are high for Sr, REE (particularly MREE), and Y, large for Th, U, and V, generally low for HFSE, and variable for other LILE. The comparison of measured Min/L D values for Campi Flegrei trachytes/trachyphonolites with other sets of partition coefficients reported in literature for evolved systems suggests that a reliable data set for magma evolution modeling requires: (1) a thorough preliminary selection of natural samples; (2) the adoption of accurate microanalytical techniques; (3) the direct measurement of Min/L D values for each specific melt composition.

Due to the similar ionic radius of K + and NH 4 + , K-silicates can incorporate a significant amount of NH4. As tourmaline is able to accommodate K in its crystal structure at high and ultrahigh pressure, we test if this also holds true for NH 4 . Piston-cylinder experiments in the system (NH 4 ) 2 O-MgO-SiO 2 -Al 2 O 3 -B 2 O 3 -H 2 O at 4.0 GPa, 700 °C, with B 2 O 3 and NH 4 OH in excess produce an assemblage of tourmaline, phengite, and coesite. The tourmaline crystals are up to 10 × 40 μm in size. EMP analyses indicate that the tourmalines contain 0.22 (±0.03) wt% (NH 4 ) 2 O and are solid solutions mainly along the magnesio-foitite and “NH 4 -dravite” join with the average structural formula X [(NH 4 ) 0.08(1) o 0.92(1) ] Y [Mg 2.28(8) Al 0.72(8) ] Z [Al 5.93(6) Si 0.07(6) ] T [Si 6.00(5) O 18 ](BO 3 ) 3 (OH) 4 . NH 4 incorporation is confirmed by characteristic <N-H> stretching and bending modes in the IR-spectra of single crystals on synthetic tourmaline. Further evidence is the increased unit-cell parameters of the tourmaline [a = 15.9214(9) Å, c = 7.1423(5) Å, V = 1567.9(2) Å 3 ] relative to pure magnesio-foitite. Incorporation of NH 4 in natural tourmaline was tested in a tourmaline-bearing mica schists from a high-P/low-T (>1.2 GPa/550 °C) metasedimentary unit of the Erzgebirge, Germany, rich in NH 4 . The NH 4 -concentrations in the three main NH4-bearing phases are: biotite (~1400 ppm) > phengite (~700 ppm) > tourmaline (~500 ppm). This indicates that tourmaline can act as important carrier of nitrogen between the crust and the deep Earth, which has important implications for a better understanding of the large-scale light element cycle.

The distribution of sulfur in the system Na 2 O-K 2 O-CaO-Al 2 O 3 -SiO 2 -H 2 O-S was investigated at 2 kbar, 750-950 °C, and oxygen fugacities ranging from the Co-CoO to the Re-ReO 2 buffer. Anhydrite (CaSO 4 ) crystallized in all the experiments conducted at oxidizing conditions (Ni-NiO + 0.5 to 1 and above). Under otherwise equal conditions, an inverse relationship between sulfur and CaO concentration was observed in melts coexisting with anhydrite, with the solubility product K = [CaO][SO 3 ] being constant, where [CaO] and [SO 3 ] are the molar fraction of CaO and SO 3 in the quenched glasses. This suggests that anhydrite dissociates upon dissolution in the melt according to CaSO 4 anhydrite = Ca 2+ melt + SO 4 2- melt . The solubility product strongly depends on temperature, with lnK = - (28 573 ± 917)/T + (11.26 ± 0.80). This corresponds to an enthalpy of dissolution of ΔH R = 237.5 ± 7.6 kJ/mol. Under reducing conditions (Co-CoO and Ni-NiO buffer), CaO has no effect on the fluid/melt partition coefficient of sulfur D s fluid/melt . At 850 °C, 2 kbar partition coefficients were 519 ± 30 at the Ni-NiO buffer and 516 ± 11 at the Co-CoO buffer, for CaO contents in the melt up to 1 wt%. These data are virtually identical to those measured in the CaO-free haplogranite system under reducing conditions. However, under more oxidizing conditions, the fluid/melt partition coefficient of sulfur appeared to have increased somewhat in the presence of CaO. This increase may, however, also be related to the fact that the final melt compositions in these runs were distinctly peraluminous. Our data show that calcium has no effect on the degassing of sulfur at reducing conditions, but it greatly reduces the amount of sulfur available for rapid degassing under oxidizing conditions by stabilizing anhydrite.

The new mineral species nuragheite, Th(MoO 4 ) 2 ·H 2 O, has been discovered in the Mo-Bi mineralization of Su Seinargiu, Sarroch, Cagliari, Sardinia, Italy. It occurs as colorless thin {100} tabular crystals, up to 200 μm in length, associated with muscovite, xenotime-(Y), and ichnusaite, Th(MoO 4 ) 2 ·3H 2 O. Luster is pearly to adamantine; nuragheite is brittle, with a perfect (100) cleavage. Owing to the very small amount of available material and its intimate association with ichnusaite, density and optical properties were not measured. Electron microprobe analysis gave (wt% = mean of six spot analyses): MoO 3 49.38, ThO 2 45.39, H 2 Ocalc 3.09, total 97.86. On the basis of eight O atoms per formula unit and assuming one H 2 O group, in agreement with the crystal structure data, the chemical formula of nuragheite is Th 1.00 Mo 2.00 O 8 ·H 2 O. Main diffraction lines, corresponding to multiple hkl indices, are [d in Å (relative visual intensity)]: 5.28 (m), 5.20 (m), 5.04 (m), 4.756 (m), 3.688 (m), 3.546 (vs), 3.177 (s), 3.024 (m). The crystal structure study gives a monoclinic unit cell, space group P2 1 /c, with a = 7.358(2), b = 10.544(3), c = 9.489(2) Å, β = 91.88(2)°, V = 735.8(2) Å 3 , Z = 4. The crystal structure has been solved and refined to a final R 1 = 0.078 on the basis of 1342 “observed” reflections [Fo > 4σ(F o )]. It consists of (100) layers formed by ninefold-coordinated Th-centered polyhedra and Mo-centered tetrahedra. Its crystal structure is discussed in relation to that of ichnusaite and that of synthetic orthorhombic Th(MoO 4 ) 2 . The relationship between the progressive loss of water in the interlayer and the layer topology passing from ichnusaite through nuragheite to synthetic (ThMoO 4 ) 2 is examined. Nuragheite, the second thorium molybdate reported so far in nature, adds new data to the understanding of the crystal chemistry of actinide molybdates potentially forming during the alteration of spent nuclear fuel and influencing the release of radionuclides under repository conditions.

Confirmation of structural H 2 O in apatites using 2 H solid state NMR spectroscopy has been followed by the determination of the number of molecules of H 2 O per unit cell (MPUC) using thermal gravimetric analysis (TGA) in 10 series of carbonated apatites [CMApX; M 10 (PO 4 ) 6 X 2 = MApX] containing the divalent cations (M) calcium, strontium, barium, and lead, and monovalent anions (X) OH - , F - , and Cl - . For many of the series, the average MPUC ranges from ca. 1.5-2.5 and is independent of the concentration (wt%) of carbonate. For other series, the average MPUC is as low as ca. 0.8 or as high as ca. 4.0. We have found for six of the series, i.e., those in which carbonate predominantly (>90%) substitutes for phosphate that the average MPUC correlates with cation and anion atomic radii, with unit-cell axial lengths, and, especially, with our calculations of the void space available in the c-axis channels. We speculate that the volume of the channels in apatites affects the ability of H 2 O to occupy channel sites. In most low-temperature apatites of the type M 10 (PO 4 ) 6 X 2 that have been studied, carbonate prefers to substitute for phosphate (B-type substitution) rather than for monovalent anions in channel sites (A-type substitution), although computer simulations indicate that carbonate is more thermodynamically stable in the channel sites rather than the phosphate sites. In apatites with nearly total B-type carbonate substitution, there is no relationship between the number of molecules of H 2 O in the channels and the weight percent carbonate in the apatite. This lack of correlation would be expected when there is no competition within the channel between H 2 O and carbonate occupancy. In apatites with greater channel volumes, however, we infer that increased ease of carbonate incorporation in the channels also increases competition between H 2 O and carbonate. The originally incorporated amount of H 2 O is diminished to accommodate the thermodynamically favored carbonate ion substitution in the channels. We further speculate that these scenarios are most easily rationalized by incorporation of H 2 O early in the formation of nascent crystallites of apatites formed in aqueous solution, with carbonate entering the newly formed channels later and, in some cases, with difficulty.

Fluorine and chlorine X‑ray count rates are known to vary significantly during electron probe microanalysis (EPMA) of apatite. Since the rate, timing, and magnitude of this variation are a function of apatite orientation and composition, as well as EPMA operating conditions, this represents a significant problem for volatile element analysis in apatite. Although the effect is thought to be an intrinsic crystallographic response to electron-beam exposure, the mechanisms and causes of the count rate variability remain unclear. We tackle this by examining directly the effects of electron-beam exposure on apatite, by performing secondary ion mass spectrometry (SIMS) depth profiles of points previously subject to electron-beam irradiation. During irradiation of fluorapatite, oriented with the c-axis parallel to the electron beam, halogens become progressively concentrated at the sample surface, even under a relatively low power (15 nA, 10-15 kV) beam. This surface enrichment corresponds to an observed increase in EPMA FKa X‑ray count rates. After prolonged irradiation, the surface region starts to lose halogens and becomes progressively depleted, corresponding with a drop in EPMA count rates. Under normal EPMA operating conditions there is no halogen redistribution in fluorapatite oriented with the c-axis perpendicular to the electron beam, or in chlorapatite. We infer that anionic enrichment results from the migration of halogens away from a center of charge build-up caused by the implantation of electrons from the EPMA beam, assisted by the thermal gradient induced by electron-matter interactions. The process of surface enrichment is best explained by halogen migration through interstitial crystallographic sites in the c-axis channel. This suggests that once the thermal and electric fields are removed, halogens may relax back to their original positions on very long timescales or with sample heating.

The Mg-suite represents an enigmatic episode of lunar highlands magmatism that presumably represents the first stage of crustal building following primordial differentiation. This review examines the mineralogy, geochemistry, petrology, chronology, and the planetary-scale distribution of this suite of highlands plutonic rocks, presents models for their origin, examines petrogenetic relationships to other highlands rocks, and explores the link between this style of magmatism and early stages of lunar differentiation. Of the models considered for the origin of the parent magmas for the Mg-suite, the data best fit a process in which hot (solidus temperature at ≥2 GPa = 1600 to 1800 °C) and less dense (ρ ~3100 kg/m 3 ) early lunar magma ocean cumulates rise to the base of the crust during cumulate pile overturn. Some decompressional melting would occur, but placing a hot cumulate horizon adjacent to the plagioclase-rich primordial crust and KREEP-rich lithologies (at temperatures of <1300 °C) would result in the hybridization of these divergent primordial lithologies, producing Mg-suite parent magmas. As urKREEP (primeval KREEP) is not the “petrologic driver” of this style of magmatism, outside of the Procellarum KREEP Terrane (PKT), Mg-suite magmas are not required to have a KREEP signature. Evaluation of the chronology of this episode of highlands evolution indicates that Mg-suite magmatism was initiated soon after primordial differentiation (<10 m.y.). Alternatively, the thermal event associated with the mantle overturn may have disrupted the chronometers utilized to date the primordial crust. Petrogenetic relationships between the Mg-suite and other highlands suites (e.g., alkali-suite and magnesian anorthositic granulites) are consistent with both fractional crystallization processes and melting of distinctly different hybrid sources.

The pressure-dependent modification of the Na-O coordination environment in albite glass is studied in situ to 2 GPa using high-pressure solid-state 23Na nuclear magnetic resonance spectroscopy. Compression of the glass at ambient-temperature results in shortening of the Na-O bond distance. The concomitant decrease in volume of the local Na-O coordination environment alone can account for the bulk compressibility of albite glass at 300 K. These results provide the first direct experimental evidence of a collapse of the open aluminosilicate framework that helps explain previously reported densification of aluminosilicate glasses and liquids at relatively low pressures without accompanying change in the average coordination number of the network forming Al and Si cations. Such structural changes at relatively low pressures may have far reaching implications for the mechanistic understanding of compressibility and viscosity anomalies characteristic of open tetrahedral aluminosilicate network glasses and melts of geological importance.

Aluminum hydroxysulfate, AlSO 4 (OH), is postulated to play a vital role in controlling the solubility of aluminum in sulfate-rich acidic soils and ground waters, but it has not yet been confirmed in nature. This study reports the synthesis of an AlSO 4 (OH) crystal at 700 °C and ~1.0 GPa in a hydrothermal diamond-anvil cell from a mixture of 95% H 2 SO 4 and Al 2 O 3 powder and its structure determination from single-crystal X‑ray diffraction data. AlSO 4 (OH) is monoclinic with space group C 2 /c and unitcell parameters a = 7.1110(4), b = 7.0311(5), c = 7.0088(4) Å, b = 119.281(2)°, and V = 305.65(3) Å 3 . Its crystal structure is characterized by kinked chains of corner-sharing AlO 6 octahedra that run parallel to the c-axis. These chains are linked together by SO 4 tetrahedra and hydrogen bonds, forming an octahedral-tetrahedral framework. Except for the numbers and positions of H atoms, AlSO 4 (OH) is isostructural with the kieserite-type minerals, a subgroup of the titanite group of minerals. A comparison of powder X‑ray diffraction patterns indicates that our AlSO 4 (OH) is the same as that obtained by Shanks et al. (1981) through hydrolysis of Al 2 (SO 4 ) 3 solutions at temperatures above 310 °C. To date, AlSO 4 (OH) has been synthesized only at temperatures above 290 °C, implying that it may not stable in low-temperature environments, such as acidic soils and mine waters. The possible environments to find Al(OH)SO 4 may include places where sulfur-rich magma-derived fluids react with aluminous rocks under elevated temperature and pressure, and on Venus where a sulfur-rich atmosphere interacts with surface rocks at temperatures above 400 °C.

This New Mineral Names has entries for nine new minerals, including adachiite, dymkovite, ferroindialite, grandaite, iwateite, kitagohaite, rauchite, torrecillasite, and zvyaginite.