Volume 98, Issue 2-3

We have investigated the high-pressure behavior of low-cristobalite form of AlPO 4 (c-AlPO 4 ) using a combination of Raman scattering, synchrotron powder X-ray diffraction, and classical molecular dynamics simulations. Our experiments indicate that under non-hydrostatic conditions c-AlPO 4 initially transforms to a monoclinic phase, which then transforms to the Cmcm phase via an intermediate, disordered structure. In contrast, X-ray diffraction measurements made under hydrostatic conditions show that the ambient structure transforms directly to the Cmcm phase. Our classical molecular dynamics simulations, carried out under hydrostatic conditions, also show that c-AlPO 4 directly transforms to the Cmcm phase at ~13 GPa.

Hydrokenomicrolite, (□,H 2 O) 2 Ta 2 (O,OH) 6 (H 2 O) or ideally □ 2 Ta 2 [O 4 (OH) 2 ](H 2 O), is a new microlite-group mineral approved by the CNMNC (IMA 2011-103). It occurs as an accessory mineral in the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. Associated minerals are: microcline, albite, quartz, muscovite, spodumene, “lepidolite”, cassiterite, tantalite-(Mn), monazite-(Ce), fluorite, “apatite”, beryl, “garnet”, epidote, magnetite, gahnite, zircon, “tourmaline”, bityite, and other microlite-group minerals under study. Hydrokenomicrolite occurs as euhedral octahedral crystals, occasionally modified by rhombododecahedra, untwinned, from 0.2 to 1.5 mm in size. The crystals are pinkish brown and translucent; the streak is white, and the luster is adamantine to resinous. It is non-fluorescent under ultraviolet light. Mohs hardness is 4½-5, tenacity is brittle. Cleavage is not observed; fracture is conchoidal. The calculated density is 6.666 g/cm 3 . The mineral is isotropic, n calc = 2.055. The infrared spectrum contains bands of O-H stretching vibrations and H-O-H bending vibrations of H 2 O molecules. The chemical composition (n = 3) is [by wavelength-dispersive spectroscopy (WDS), H 2 O calculated from crystal-structure analysis, wt%]: CaO 0.12, MnO 0.27, SrO 4.88, BaO 8.63, PbO 0.52, La 2 O 3 0.52, Ce 2 O 3 0.49, Nd 2 O 3 0.55, Bi 2 O 3 0.57, UO 2 4.54, TiO 2 0.18, SnO 2 2.60, Nb 2 O 5 2.18, Ta 2 O 5 66.33, SiO 2 0.46, Cs 2 O 0.67, H 2 O 4.84, total 98.35. The empirical formula, based on 2 cations at the B site, is [□ 0.71 (H 2 O) 0.48 Ba 0.33 Sr 0.27 U 0.10 Mn 0.02 Nd 0.02 Ce 0.02 La 0.02 Ca 0.01 Bi 0.01 Pb 0.01 ] Σ2.00 (Ta 1.75 Nb 0.10 Sn 0.10 Si 0.04 Ti 0.01 ) Σ2.00 [(O 5.77 (OH) 0.23 ] Σ6.00 [(H 2 O) 0.97 Cs 0.03 ] Σ1.00 . The strongest eight X-ray powderdiffraction lines [d in Å(I)(hkl)] are: 6.112(86)(111), 3.191(52)(311), 3.052(100)(222), 2.642(28)(400), 2.035(11)(511)(333), 1.869(29)(440), 1.788(10)(531), and 1.594(24)(622). The crystal structure refinement (R 1 = 0.0363) gave the following data: cubic, Fd3̄m, a = 10.454(1) Å, V = 1142.5(2) Å 3 , Z = 8. The Ta(O,OH) 6 octahedra are linked through all vertices. The refinement results and the approximate empirical bond-valences sums for the positions A (1.0 v.u.) and Y′ (0.5 v.u.), compared to valence calculations from electron microprobe analysis (EMPA) and ranges expected for H 2 O molecules, confirm the presence of H 2 O at the A(16d) site and displaced from the Y(8b) to the Y′(32e) position. The mineral is characterized by H 2 O dominance at the Y site, vacancy dominance at the A site, and Ta dominance at the B site.

Fluor-elbaite, Na(Li 1.5 Al 1.5 )Al 6 (Si 6 O 18 )(BO 3 ) 3 (OH) 3 F, is a new mineral of the tourmaline supergroup. It is found in miarolitic cavities in association with quartz, pink muscovite, lepidolite, spodumene, spessartine, and pink beryl in the Cruzeiro and Urubu mines (Minas Gerais, Brazil), and apparently formed from late-stage hydrothermal solutions related to the granitic pegmatite. Crystals are bluegreen with a vitreous luster, sub-conchoidal fracture and white streak. Fluor-elbaite has a Mohs hardness of approximately 7.5, and has a calculated density of about 3.1 g/cm 3 . In plane-polarized light, fluor-elbaite is pleochroic (O = green/bluish green, E = pale green), uniaxial negative. Fluor-elbaite is rhombohedral, space group R3̄m, a = 15.8933(2), c = 7.1222(1) Å, V = 1558.02(4) Å 3 , Z = 3 (for the Cruzeiro material). The strongest eight X-ray-diffraction lines in the powder pattern [d in Å(I)(hkl)] are: 2.568(100)(051), 2.939(92)(122), 3.447(67)(012), 3.974(58)(220), 2.031(57)(152), 4.200(49)(211), 1.444(32)(642), and 1.650(31)(063). Analysis by a combination of electron microprobe, secondary ion mass spectrometry, and Mössbauer spectroscopy gives SiO 2 = 37.48, Al 2 O 3 = 37.81, FeO = 3.39, MnO = 2.09, ZnO = 0.27, CaO = 0.34, Na 2 O = 2.51, K 2 O = 0.06, F = 1.49, B 2 O 3 = 10.83, Li 2 O = 1.58, H2O = 3.03, sum 100.25 wt%. The unit formula is: X(Na 0.78 □ 0.15 Ca 0.06 K 0.01 ) Y (Al 1.15 Li 1.02 Fe 2+ 0.46 Mn 2+ 0.28 Zn 0.03 ) ZAl 6 T(Si 6.02 O 18 ) B (BO 3 ) 3 V (OH) 3 W (F 0.76 OH 0.24 ). The crystal structure of fluor-elbaite was refined to statistical indices R1 for all reflections less then 2% using MoKα X-ray intensity data. Fluor-elbaite shows relations with elbaite and tsilaisite through the substitutions W F ↔ W OH and Y (Al + Li) + W F ↔ 2 Y Mn 2+ + W OH, respectively.

The effects of water concentration and degassing history on the development of spherulites and flow banding were examined in three middle Tertiary rhyolitic lava flows from the Atascosa Mountains of southern Arizona. The Hell’s Gate lava flow and the Atascosa lava flow host spherulites of strongly contrasting texture, and neither are flow banded. The Sycamore Canyon lava flow is a flowbanded rhyolite that hosts two populations of spherulites. Spherulites in the Hell’s Gate lava flow consist of two to four generations of bladed radiating alkali feldspar crystals that increase in water concentration along their length. Needle-like radiating feldspar crystals in spherulites in the Atascosa and Sycamore Canyon lava flows are in some cases punctuated by concentric rinds of glass that are reservoirs for water rejected by the feldspar crystals. The differences in spherulite crystal morphology between the Sycamore Canyon and Atasocosa flows (both needle-like) and the Hell’s Gate flow (bladed) may reflect a more rapid cooling rate of the Sycamore Canyon and Atascosa flows. Thick gray flow bands in the Sycamore Canyon lava flow host higher water concentrations than thin orange flow bands, suggesting that flow bands are zones of greater and lesser volatile concentration, deformed by stretching of the flowing magma. Temperature was uniform across the light and dark flow bands of the Sycamore Canyon flow, indicating that water concentration, one of the variables that controls diffusion coefficients, rather than temperature, controlled spherulite size in this case. Phenocrysts in the Hell’s Gate lava flow are strongly resorbed, probably as a result of magma ascent along a nearadiabatic gradient that resulted in exsolution of water from the melt, and subsequent dissolution of existing quartz phenocrysts by the water-rich melt. Resumption of crystallization of anhydrous phases such as quartz and feldspar would have further enriched the melt in water, facilitating the growth of spherulites. Spherulites in two of the lava flows (Sycamore Canyon and Hell’s Gate) increase in water concentration from core to rim, as would be expected in spherulites growing in melt enriched in water rejected by the growing feldspar crystals. Spherulites in the Atascosa rhyolite flow decrease slightly in water concentration from core to rim, possibly because the magma degassed during spherulite growth. Calculation of water concentration profiles in spherulites from all three rhyolite flows on the basis of Rayleigh fractionation of water between sanidine and rhyolitic melt shows that the very high water concentrations in spherulites (typically >0.6 × water concentration in surrounding glass) cannot be accounted for by Rayleigh fractionation. Instead it is likely that sanidine incorporated water as fluid inclusions and/or as water clusters during rapid crystal growth. Water concentration profiles in the glass surrounding spherulites do not preserve the high concentration zone at the spherulite boundary that has been observed in younger lava flows, so that spherulite growth rates cannot be calculated on the basis of mass-balance calculations of distribution of water during spherulite growth. Rather, the water concentration profile in the surrounding glass is a half plateau, the height of which is approximately equivalent to the far-field water concentration in the surrounding glass, indicating that water that accumulated at the spherulite/magma boundary diffused sufficiently rapidly to equilibrate with the surrounding magma as the lava flow cooled.

Biological activity plays a substantial role in the geochemistry of the Earth’s surface. Particularly interesting are effects on clay formation because clays are abundant and have high surface-to-volume ratio, resulting in clays making up a large fraction of the overall mineral-fluid interface and having an effective control of mineral reactions. Thus, biological control on clay composition would affect element budget globally and the mineralogy of subsequent diagenetic processes. Biological acceleration of clay production would result in enhanced clay control of mineral reactions and faster organic C sequestration, by adsorption on clay minerals, with implications for the C and related cycles. We investigated the combined effect of microbial activity and water chemistry on the composition of neoformed clay by reacting volcanic glass with natural waters covering a large composition range (fresh water from a lake and a spring, seawater, and hypersaline water). The microbes (bacteria, fungi, and algae) were totally or partially identified using molecular and microscopy techniques. The solid alteration products were analyzed using cryo-SEM to investigate the mineral-microbe interface and TEM-AEM to study the composition of the neoformed clay. The solution chemistry was also investigated. We found that clay composition was controlled mainly by glass chemistry, rather than biological activity, through a mechanism of in situ transformation. The resulting clay was Al-rich (dioctahedral composition). In one case (inorganic experiment, freshwater lake), the specific inorganic conditions of pH and Mg and Si concentration promoted formation of Mg-rich (trioctahedral clay). Microbes, however, did influence clay composition by confining glass grains in biofilms where water chemistry is significantly different from the bulk solution. Alteration in such conditions generated significant amounts of trioctahedral, Mg-rich clay in the hypersaline water experiment, whereas it favored production of dioctahedral, Alrich clay in the freshwater lake experiment. It is thus demonstrated that biofilms can exert an effective control on clay mineralogy.

Phase transitions in Al 2 O 3 between corundum Rh 2 O 3 (II)-type and CaIrO 3 -type (post-perovskitetype) phases were examined at high pressure and high temperature in a laser-heated diamond-anvil cell (DAC) based on in situ X-ray diffraction measurements. The locations of corundum-Rh 2 O 3 (II) and Rh 2 O 3 (II)-CaIrO 3 boundaries were precisely determined by conducting both forward and backward reaction experiments. The results demonstrate that corundum undergoes a phase transition to Rh 2 O 3 (II)-type structure above 106 GPa at 1800 K with a negative Clapeyron slope of -6.5 ± 1.5 MPa/K, generally consistent with earlier experimental and theoretical works. The Rh 2 O 3 (II)-type phase further transforms into CaIrO 3 -type above 170 GPa at 2300 K, indicating the transition pressure much higher than earlier experimental work but in agreement with reported GGA calculations. The Clapeyron slope of this phase transition was found to be high negative (-20 ± 5 MPa/K).

The vectorial bond-valence model (VBVM) describes the spatial distribution of bonds to each atom in a system in terms of the vector sum of the incident bond valences. It has been applied in the past to cations not subject to electronic structure effects (e.g., lone-pair or Jahn-Teller effects) in which case the expectation is that the vector sum will be approximately zero. Here we analyze 178 simpleoxide crystal structures and show that the vectorial bond-valence sum is a predictable function of the atomic valence (oxidation state) of each atom and the valence of the strongest bond to atoms for which second-order Jahn-Teller and lone-pair effects play a role in determining molecular geometry. Outliers are uniformly metastable or unstable under ambient conditions, suggesting that deviation from ideal vectorial bond-valence sums might be used as a proxy for some aspect of structural potential energy. These results are all strictly in harmony with the VSEPR model of molecular geometry, but may allow for more quantitative prediction.

Geometrical modeling of radiation damages zones from α recoil and fission that accounts for their elongate nature provides new estimates of the doses required to reach percolation and full connectivity in zircon. Alpha recoil track damage percolates at doses from 2.5-3.1 × 10 16 α/g based on our calculations, about two orders of magnitude lower than previous estimates, with the difference partially due to elongation and partially due to decay chains creating pre-made networks of connected tracks. This dose level is far below that required for metamictization, and suggests that α recoil track percolation has no effect on macroscopic or unit-cell properties, at least as measured to date. However, fission tracks percolate at a dose of approximately 1.9 × 10 18 α/g, the approximate level formerly ascribed to α recoil damage percolation and correlating with various transitions in material properties, such as an inflection in the relationship between dose and macroscopic swelling. Consideration of the undamaged regions between damage zones indicates that c-axis-parallel channels are frequently interrupted, at the micrometer scale at very low doses and tens of nanometers at usual doses in natural zircon, with the probable effect of decreasing diffusivity anisotropy. The percolation and further interconnectivity of α recoil damage corresponds with a general minimum in diffusivity and maximum in closure temperature in zircon, indicating that α recoil damage percolation does not make a grain “leaky”, but instead quite the opposite. Instead, the onset of poor He retentivity at high damage levels correlates with fission-track percolation. Some of these results are non-intuitive with respect to the trapping model of He diffusivity reduction, and the alternative mechanism of tortuosity is discussed.

The crystal structure of the rare, spinel-related Sb mineral filipstadite from Långban, Filipstad district, Värmland, Sweden, has been solved and refined in the space group Fd3̄m [a = 25.9300(6) Å, V = 17434.4(5) Å 3 , and Z = 216] and refined to R = 4.41% for 681 F o > 4σ(F o ) using MoKα X-ray data. The structure of filipstadite is topologically identical to the spinel-type structure with cations occupying 1/8 of the tetrahedral (T) and 1/2 of the octahedral (M) interstices of a cubic close-packing of oxygen atoms. Due to the cation ordering, which leads to the tripling of the unit-cell edge, the M and T sites of the spinel-type structure split into six and five independent sites, respectively. Chemical composition was determined by electron microprobe. The fractions of major cations obtained from chemical analysis were distributed between T and M sites taking into account the weighted electron number at both T and M sites, and minimizing the discrepancy between the calculated and the observed overall <M-O> distance. Cations present in minor amounts were assigned on the basis of their known site preference. The obtained populations (2M = Mn 2+ 0.56 Mg 0.76 Fe 3+ 0.16 Al 0.02 Sb 5+ 0.50 ; T = Mn 2+ 0.60 Mg 0.07 Fe 3+ 0.30 Zn 0.02 Si 4+ 0.01 ) were then tentatively distributed among the individual M and T sites on the basis of crystal chemical considerations.

The sound velocities (nv p , v p , v s ) and refractive index n of four haplogranitic glasses and melts have been measured as a function of temperature by Brillouin scattering spectroscopy. The measurements were conducted at GHz frequency, through the glass transition temperature (T g ), using both platelet and backscattering geometries. The compositions of the four haplogranites are based on the addition of ~5 wt% each of the components Li 2 O, F 2 O -1 , Na 2 O, and K 2 O to a haplogranitic (HPG8) composition. Marked changes in slope and sign are observed in the temperature dependences of sound velocities (nv p , v p , v s ) as a function of composition. The glass transition temperatures T g of the haplogranite samples are determined from distinct slope changes of sound velocities (v p and v s ) vs. temperature. The lithium-enriched glass has the lowest glass transition temperature (466 °C), while the potassic glass has the highest glass transition temperature (575 °C). The unrelaxed bulk moduli vary markedly with composition below the glass transition, as do their temperature dependencies: the bulk moduli of the F- and Na-rich glasses have positive shifts with temperature. For comparison, the shear moduli have relatively similar temperature dependences below T g for different alkali contents. At temperatures above the glass transition, the temperature derivatives of the bulk moduli, which for these frequencies reflect the vibrational compressibilities of the liquids, shift to more negative values. However, the compositional range over which the bulk moduli undergo positive or small negative temperature shifts of the vibrational compressibility appears to extend to NBO/T ratios near 0.3-0.4, or spanning most haplogranite compositions.

Hydrogen isotope fractionation between water-saturated silicate melt and silicate-saturated aqueous fluid has been determined experimentally by using vibrational spectroscopy as the analytical tool. The measurements were conducted in situ with samples at the high temperature and pressure of interest in an externally heated diamond cell in the 450-800 °C and 101-1567 MPa temperature and pressure range, respectively. The starting materials were glass of Na-silicate with Na/Si = 0.5 (NS4), an aluminosilicate composition with 10 mol% Al 2 O 3 and Na/(Al+Si) = 0.5 (NA10), and a 50:50 (by volume) H 2 O:D 2 O fluid mixture. Platinum metal was used to enhance equilibration rate. Isotopic equilibrium was ascertained by using variable experimental duration at given temperature and pressure. In the Al-free NS4 system, the enthalpy of the D/H equilibrium of fluid is 3.1 ± 0.7 kJ/mol, whereas that of coexisting melt equals 0 within error. For NA10 fluids the ΔH = 5.2 ± 0.9 kJ/mol, whereas for coexisting NA10 melt, ΔH is near 0 within error. For the exchange equilibrium between melt and coexisting fluid, H 2 O(melt)+D 2 O(fluid) = H 2 O(fluid)+D 2 O(melt) the ΔH = 4.6 ± 0.7 and 6.5 ± 0.7 kJ/ mol for NS4 and NA10 compositions, respectively. The D/H fractionation between melt and fluid is affected significantly by the positive temperature- and pressure-dependence of silicate solubility and silicate structure in silicate-saturated aqueous fluids. Water in melts is much less important than silicate in aqueous fluid because even at the lowest temperature and pressure conditions studied (450 °C/101 MPa), the water content in the melt is so high (>4 wt%) that further increase in total water by increasing temperature and pressure does not affect the silicate melt structure significantly. This is because most of the water in this concentration range is dissolved in molecular form.

We report mineral assemblages from three clasts in the Northwest Africa 801 CR chondrite. The clasts, 1-3 mm in size, are ellipsoidal to irregular shaped, and show similar granular texture. The constituent minerals in the clasts are omphacite-rich clinopyroxene and pyrope-rich garnet, in addition to olivine and orthopyroxene. The omphacite contains jadeite (34 mol%) and diopside-hedenbergite (37%), and a significant amount of an enstatite-ferrosilite component (19%), which distinguishes it from terrestrial omphacite. The omphacite has a disordered C2/c structure. Graphite, phlogopite, chlorapatite, Fe-Ni metal, troilite, and pentlandite are present as minor minerals in the clasts. The minerals commonly found in chondrites, such as plagioclase and spinel group minerals, are not found in these clasts. Aluminum and sodium in the clasts are completely partitioned into omphacite and garnet. The mineral assemblages and compositions of the clasts are similar to those in terrestrial eclogite, except for the occurrence of olivine and some mineral chemistry, and this is the first discovery of an extraterrestrial eclogitic mineral assemblage. The clasts formed under high-pressure conditions, 2.8-4.2 GPa and 940-1080 °C, as estimated from a set of conventional geothermobarometers, indicative of formation in a large parent body. Another possibility is impact-induced origin, although the formation conditions would have been different from those for known shock veins. Meteorites usually consist of minerals that formed under low-pressure conditions, except for ultrahigh-pressure minerals found in shock veins. However, this study suggests that the pressure conditions for meteorite formation vary much wider than previously understood.

An understanding of the interaction mechanisms between exchangeable cations and layered silicates is of interest from both a basic and an applied point of view. Among 2:1 phyllosilicates, a new family of swelling high-charge synthetic micas has been shown to be potentially useful as decontaminant. However, the location of the interlayer cations, their acidity and the water structure in the interlayer space of these silicates are still unknown. The aim of this paper was therefore to study the hydration state of the interlayer cations in the interlayer space of high-charge expandable micas and to evaluate the effect that this hydration has on the swelling and acidity behavior of these new materials. To achieve these objectives, three synthetic micas with different charge density total layer charges (ranging between 2 and 4 per unit cell) and with five interlayer cations (Na + , Li + , K + , Mg 2+ , and Al 3+ ) were synthesized and their hydration state, interlayer space, and acidity analyzed by DTA/TG, XRD, and 1 H MAS NMR spectroscopy. The results showed that the hydration state depends on both the layer charge and the nature of the interlayer cation. A high participation of the inner-sphere complexes in the highly charged confined space has been inferred and proposed to induce Brønsted acidity in the solid.

Mg-Ca carbonates are an important group of industrial minerals, which frequently occur intimately intermixed in natural settings and are traditionally assessed for phase purity by X-ray diffraction (XRD). In this study Raman spectroscopy is employed to quantify the modal abundance of hydromagnesite [Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O], huntite [CaMg 3 (CO 3 ) 4 ], dolomite [MgCa(CO 3 ) 2 ], and magnesite [MgCO 3 ], in powdered mixtures constructed from fabricated reference materials. Particle size distributions were assessed by scanning electron microscopy and laser diffraction. Raman analyses performed using a portable instrument were conducted at 25 °C and at atmospheric pressure. XRD was employed to validate the accuracy and precision of Raman measurements. Monovariable and multivariable methods were employed to provide quaternary quantification from the spectroscopic data. For monovariable calibration the amplitude of the peaks was plotted against the measured weight ratios of the four mineral phases. Overlapping bands were resolved using the Gaussian Lorentzian method. Chemometric methods were used to perform the multivariable calibration. The overall lowest error on component values was obtained by principal component regression with application of standard normal variate correction. The quantifications derived by Raman spectroscopy and XRD show close agreement. Hence, evidence suggests that a reliable four-way calibration program to screen the purity of carbonate assemblages can be constructed, providing particle size effects are constrained and spectroscopic operating conditions are uniform.

Apatite minerals draw the attention of many researchers not only in mineralogy, but also in biology, biochemistry, and medicine because hydroxylapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] is the main component of the mineral phase of mammalian bones. However, in nature this mineral is mostly present with various stoichiometric defects. The carbonate ion is found commonly in its structure where it can occupy different crystallographic sites; however, its configurational energy and relative orientation in the apatite lattice is still debated. In this work, bulk structural features of hexagonal hydroxylapatite (space group P6 3 ) and type A carbonated apatite [Ca 10 (PO 4 ) 6 (CO 3 ), space group P1] have been modeled by density function method using the hybrid B3LYP functional and an all-electron polarized double-ζ quality Gaussian-type basis set using the CRYSTAL09 computer program. The effect on the structural parameters due to the adoption of the present all-electron basis set for the Ca ion compared to the pseuodpotential adopted in previous work has also been discussed. Different orientations of the carbonate ion in the apatite unit cell have been considered. The B3LYP functional and Gaussian-type basis set with polarization have been adopted. The geometry of the model (lattice parameters and internal coordinates) has been fully optimized and resulted in very good agreement with XRD data reported in literature that suggest a “close” configuration (type A1) of the carbonate ion, i.e., with a C-O bond perpendicular to the c -axis of the apatite cell.

Pseudobrookite microphenocrysts occur in cognate inclusions in the ~305 ka Coleman Pinnacle hornblende andesite flow from the Mount Baker volcanic field, Washington. Pseudobrookites are associated with hornblende phenocrysts and glomerophyric clusters of orthopyroxene, clinopyroxene, plagioclase, ilmenite, titanomagnetite, apatite, and zircon in a matrix of fresh rhyolitic glass. Grains of pseudobrookite are rimmed by or intergrown with ilmenite. These textures are analogous to those observed between armalcolite and ilmenite in high-Ti lunar basalts. In a unique occurrence, pseudobrookite, and titanomagnetite form a symplectitic intergrowth surrounding a core of ilmenite. Mass balance calculations show that the pseudobrookite + titanomagnetite assemblage is not an isochemical decomposition of ilmenite. In the TiO 2 -FeO-Fe 2 O 3 system (Mg-free), pseudobrookite and titanomagnetite solid solutions do not coexist. However, all three Fe-Ti oxides in the symplectitic assemblage contain significant amounts of Mg. In the TiO 2 -MgO-FeO-FeO 1.5 system at high oxygen fugacities, the Mg-rich pseudobrookite + titanomagnetite assemblage is stable relative to the conjugate pair of Mg-bearing ilmenite solid solutions. At lower f O2 , Fe 2+ increases, Mg/(Mg+Fe 2+ ) (Mg no.) decreases and the conjugate ilmenite pair becomes the stable assemblage at Mg no. < ~0.6. The compositions of coexisting ilmenite + titanomagnetite pairs in the Coleman Pinnacle andesite yield T = 900-1000 °C and f O2 = NNO + 1.5 to + 1.75, one of the highest redox states on record for arc magmas. The calculated fO2 range is consistent with the composition of the ilmenite in equilibrium with pseudobrookite ± rutile and with Fe 3+ -rich cores in hornblende phenocrysts.

Pyrochlore minerals are common accessory phases in the syenite and nepheline syenite rocks of the Motzfeldt alkaline center, Gardar Province, South Greenland, and are of important economic interest due to their exceptional ability to host various high field strength elements. In this study pyrochlore from two distinct intrusive units within the Motzfeldt Center have been studied. The largely homogeneous syenite and nepheline syenite rocks of the Flinks Dal formation host oscillatory and sector-zoned pyrochlore, which have experienced minor alteration in the presence of high-temperature, dominantly juvenile magmatic fluids. Alteration is characterized by variable decrease in the Na, Ca, and F contents and addition of Sr and K, accompanied by introduction of A and Y site vacancies. Pyrochlore from the more heterogeneous and intensely altered syenite rocks of the Motzfeldt Sø Formation are pervasively altered through interaction with lower temperature evolved hydrothermal fluids. During this phase of alteration cations are preferentially leached from the A and Y sites, accompanied by progressively increasing hydration. In both formations the proportion of B-site cations remains unaltered regardless of the degree of alteration. The alteration encoded in the pyrochlores of the Motzfeldt Center records the different hydrothermal conditions the two formations experienced during the subsolidus, showing how evolution of fluids within one intrusive unit can vary both spatially and temporally.

Phosphovanadylite-Ca, Ca[V 4 4+ P 2 O 8 (OH) 8 ]·12H 2 O, is a new mineral from the South Rasmussen (or South Rasmussen Ridge) phosphate mine, Soda Springs, Caribou County, Idaho. It is named as the Ca analog of phosphovanadylite, which is now renamed as phosphovanadylite-Ba. The new mineral grows on matrix containing fine-grained quartz, massive, porous fluorapatite and hydroxylapatite, framboidal pyrite, and tiny, euhedral sphalerite crystals. Other minerals directly associated with the new mineral are sincosite and native Se. Phosphovanadylite-Ca crystallized at ambient temperatures from late-stage aqueous solutions of near neutral pH under relatively reducing conditions. The mineral is cubic, space group I4̄3m, a = 15.441(11) Å, V = 3682(5) Å 3 , and Z = 6. Crystals occur as small, greenish-blue simple cubes (to 0.1 mm on edge) intergrown to form thin crusts. Penetration twinning on {111} is common. The color is bright greenish blue, the streak is very pale greenish blue, and the luster is vitreous. The Mohs hardness is estimated at 2. The new mineral is brittle with irregular fracture and no cleavage. The measured density is 2.02(3) g/cm 3 and the calculated density based on the empirical formula is 2.038 g/cm 3 . Phosphovanadylite-Ca is isotropic with n = 1.559(2). The normalized electron microprobe analysis based upon sufficient H for charge balance and 12 molecules of zeolitic H 2 O is: Na 2 O 0.22, K 2 O 0.55, CaO 5.58, SrO 0.10, BaO 0.21, Al 2 O 3 3.27, VO 2 35.85, P 2 O 5 18.78, H 2 O 35.44, Total 100.00. The empirical formula (based on 2 P and 28 O apfu) is: (Ca 0.75 K 0.09 Na 0.05 Ba 0.01 Sr 0.01 ) Σ0.91 [(V 4+ 3.27 Al 0.49 ) Σ3.76 P 2.00 O 10.23 (OH) 5.77 ]·12H 2 O. The eight strongest powder X-ray diffraction lines are [dobs in Å (hkl) I]: 11.04 (110) 97, 7.7881 (200) 100, 4.487 (222) 14, 3.1706 (422) 46, 2.749 (440) 32, 2.4576 (620) 14, 2.3426 (622) 15, and 1.8295 (822) 16. The crystal structure of phosphovanadylite-Ca (R1 = 0.027 for 171 reflections with Fo > 4σF) contains V 4 4+ O 16 polyvanadate clusters of four edge-sharing V4+O6 octahedra. The polyvanadate clusters are linked into a three-dimensional zeolite-like framework by sharing corners with PO 4 tetrahedra. The open space in the framework is dominated by H 2 O with the equivalent of one large cation pfu sharing one of the H 2 O sites. The framework is identical to that in phosphovanadylite-Ba; however, in phosphovanadylite-Ba, the dominant extra-framework cation is Ba, while in phosphovanadylite-Ca, it is Ca.

The Wentworth Pluton in the Eastern Cobequid Highlands consists principally of metaluminous to peralkaline A-type granite (~362 Ma), a large part of which was remelted by a major gabbro intrusion (~357 Ma). Magmatic minerals like allanite-(Ce), chevkinite-(Ce), zircon, and hingganite-(Y) and post-magmatic mineral phases, such as REE-bearing epidote, samarskite-(Y), aeschynite-(Y), fersmite, thorite-like phases, and hydroxylbastnäsite-(Ce), were identified. The presence of fluorine in the parental magma, indicated by whole-rock geochemical data and the presence of fluorite, increased the solubility of monazite and xenotime and thus facilitated retainment of rare metals in the magmatic system. Fractionation of allanite-(Ce) and chevkinite-(Ce) led to a melt enriched in heavy rare earth elements (HREE), from which hingganite-(Y) crystallized during late magmatic stages. The remelting of the early granite led to fluorine and sulfur release in volatile phases, which circulated with hydrothermal fluids, thus mobilizing the REE and other rare metals. Reduction of fluorine activity during the late to post-solidus crystallization resulted in the precipitation of HREE and rare metals in samarskite-(Y), thereby enriching the residual hydrothermal fluids in light rare earth elements (LREE). Post-magmatic LREE minerals, such as hydroxylbastnäsite-(Ce), either replaced earlier minerals or precipitated from these hydrothermal fluids. Carbonate fluids involved in a late regional hydrothermal circulation event along the Cobequid-Chedabucto fault (320-315 Ma) promoted Ti mobility and the formation of TiO 2 minerals and probably of aeschynite-(Y). This mineralogical diversity, in addition to the complex geological history of the pluton, provides a unique opportunity to correlate the formation of individual rare-metal minerals to different stages of pluton evolution and thus provide an insight to the formation conditions of these minerals.

Prewittite, ideally KPb 1.5 Cu 6 Zn(SeO 3 ) 2 O 2 Cl 10 , was found in the fumarole field of the second cinder cone of the North Breach of the Great fissure Tolbachik eruption (1975-1976, Kamchatka peninsula, Russia). It occurs as separate olive-green tabular crystals up to 0.2 mm in maximum dimension. It has vitreous luster and brownish-green streak. Prewittite is orthorhombic, space group Pnnm, a = 9.132(2), b = 19.415(4), c = 13.213(3) Å, V = 2342.6(9) Å 3 , Z = 4, D calc = 3.89 g/cm 3 , D meas = 3.90(2) g/cm 3 . The eight strongest lines of the powder X-ray diffraction pattern are {I [d(Å)] hkl}: 70 (8.26) 110; 60 (7.53) 101; 90 (4.111) 220, 132, 141; 100 (3.660) 212, 123; 40 (2.996) 223; 50 (2.887) 062; 40 (2.642) 322, 214; 40 (2.336) 073, 180, 244. Prewittite is biaxial (-). The optical orientation is X = a, Y = c, Z = b. The mineral has clear pleochroism: X, Y - olive green, Z - red-brown. The mineral is very brittle with the perfect cleavage on (010) and (101). The most developed crystal forms are {010}, {001}, and {101}. The chemical composition determined by the electron-microprobe is (wt%): K 2 O 1.76, PbO 21.18, CuO 33.24, ZnO 8.00, SeO 2 15.74, Cl 26.06, O=Cl -5.88, total 100.10. The empirical formula derived on the basis of O+Cl = 18 and sum of positive charges of cations equal to 26 is K 0.53 Pb 1.33 Cu 5.87 Zn 1.38 Se 1.99 O 7.67 Cl 10.33 . The crystal structure was solved by direct methods and refined to an agreement index R1 = 0.034 on the basis of 1522 independent reflections with I ≥ 2 σI . It is based upon metal oxide selenite chloride layers parallel to (010) and linked through K-Cl and Pb-Cl bonds to the K and Pb atoms located in the interlayer. The mineral name honors Charles T. Prewitt (b. 1933) in recognition of his important contributions to crystal chemistry of minerals and planetary materials.

Lucabindiite, ideally (K,NH 4 )As 4 O 6 (Cl,Br), is a new mineral found as a medium-temperature fumarole encrustation (T = 170 °C) at “La Fossa” crater of Vulcano, Aeolian Islands, Italy. The mineral deposited as aggregates of micrometer-sized hexagonal and platy crystals on the surface of the pyroclastic breccia in association with arsenolite, sal ammoniac, sulfur, and amorphous arsenic-rich sulfurite. The new mineral is colorless to white, transparent, non-fluorescent, has a vitreous luster and a white streak. The calculated density is 3.68 g/cm 3 . Lucabindiite is hexagonal, space group P6/mmm, with a = 5.2386(7) Å, c = 9.014(2) Å, V = 214.23(7) Å 3 , and Z = 1. The eight strongest reflections in the X-ray powderdiffraction data [d in Å (I) (hkl)] are: 3.20 (100) (102), 2.62 (67) (110), 4.51 (52) (002), 4.54 (30) (100), 1.97 (28) (113), 1.49 (21) (115), 1.60 (21) (212), 2.26 (19) (112). Lucabindiite’s average chemical composition is (wt%): K 2 O 5.14, As 2 O 3 84.71, Cl 3.63, Br 6.92, F 0.77, (NH 4 ) 2 O 2.73, O=F,Cl,Br -1.84, total 102.06. The empirical chemical formula, calculated on the basis of 7 anions pfu, is [K 0.51 (NH 4 ) 0.49 ] Σ1.00 As 4.00 O 5.93 (Cl 0.48 Br 0.40 F 0.19 ) Σ1.07 . According to chemical analyses and X-ray data, lucabindiite is the natural analog of synthetic phases with general formula MAs 4 O 6 X where M = K, NH 4 and X = Cl, Br, I. The crystal structure is characterized by neutral As 2 O 3 sheets arranged parallel to (001). The As atoms of two neighboring sheets point at each other and the sheets are separated by interlayer M (=K, NH 4 ) and X (=Cl, Br, F) atoms. The name is in honor of Luca Bindi (b. 1971), Professor of Mineralogy and former Head of the Division of Mineralogy of the Natural History Museum of the University of Florence. Both the mineral and the mineral name have been approved by the IMA-CNMNC Commission (IMA 2011-010).

A new mineral species, scottyite, ideally BaCu 2 Si 2 O 7 , has been found in the Wessels mine, Kalahari Manganese Fields, Northern Cape Province, South Africa. The mineral appears to have formed as a result of a hydrothermal event and is associated with wesselsite, pectolite, richterite, sugilite, and lavinskyite. Scottyite forms blocky grains with striations parallel to the c axis. Crystals are found up to 0.4 × 0.3 × 0.3 mm. No twinning is observed. The mineral is dark-blue in transmitted and under incident lights, transparent with pale blue streak and vitreous luster. It is brittle and has a Mohs hardness of 4-5; cleavage is perfect on {100} and {010} and no parting was observed. The calculated density is 4.654 g/cm 3 . Optically, scottyite is biaxial (-), with α = 1.750(1), β = 1.761(1), and γ = 1.765(1), 2V meas = 66(2)°. It is insoluble in water, acetone, or hydrochloric acid. An electron microprobe analysis produced an average composition (wt%) (8 points) of CuO 36.98(31), BaO 35.12(16), SiO 2 27.01(61), SrO 0.28(5), and Na 2 O 0.06(2), and total = 99.45(65), yielding an empirical formula (based on 7 O apfu) Ba 1.00 Sr 0.01 Na 0.01 Cu 2.04 Si 1.97 O 7 . Scottyite is the natural analog of synthetic BaCu 2 (Si,Ge) 2 O 7 , which exhibits novel one-dimensional quantum spin-1/2 antiferromagnetic properties with tunable super-exchange interactions. It is orthorhombic, with space group Pnma and unit-cell parameters a = 6.8556(2), b = 13.1725(2), c = 6.8901(1) Å, and V = 622.21(6) Å 3 . The structure of scottyite is characterized by flattened CuO 4 tetrahedra sharing corners with one another to form chains parallel to the c axis. These chains are interlinked by Si 2 O 7 tetrahedral dimers and Ba 2+ . The Ba 2+ cations are bonded to seven O atoms in an irregular coordination. The average Si-O, Cu-O, and Ba-O bond lengths are 1.630, 1.941, and 2.825 Å, respectively. Scottyite is topologically related to a group of compounds with the general formula BaM 2+ 2 Si 2 O 7 , where M = Be (barylite and clinobarylite), Fe (andrémeyerite), Mg, Mn, Co, and Zn.

Oxy-schorl (IMA 2011-011), ideally Na(Fe 2 2+ Al)Al 6 Si 6 O 18 (BO 3 ) 3 (OH) 3 O, a new mineral species of the tourmaline supergroup, is described. In Zlatá Idka, Slovak Republic (type locality), fan-shaped aggregates of greenish black acicular crystals ranging up to 2 cm in size, forming aggregates up to 3.5 cm thick were found in extensively metasomatically altered metarhyolite pyroclastics with Qtz+Ab+Ms. In Přibyslavice, Czech Republic (co-type locality), abundant brownish black subhedral, columnar crystals of oxy-schorl, up to 1 cm in size, arranged in thin layers, or irregular clusters up to 5 cm in diameter, occur in a foliated muscovite-tourmaline orthogneiss associated with Kfs+Ab+Qtz+Ms+Bt+Grt. Oxy-schorl from both localities has a Mohs hardness of 7 with no observable cleavage and parting. The measured and calculated densities are 3.17(2) and 3.208 g/cm3 (Zlatá Idka) and 3.19(1) and 3.198 g/cm 3 (Přibyslavice), respectively. In plane-polarized light, oxy-schorl is pleochroic; O = green to bluish-green, E = pale yellowish to nearly colorless (Zlatá Idka) and O = dark grayish-green, E = pale brown (Přibyslavice), uniaxial negative, ω = 1.663(2), ε = 1.641(2) (Zlatá Idka) and ω = 1.662(2), ε = 1.637(2) (Přibyslavice). Oxy-schorl is trigonal, space group R3m, Z = 3, a = 15.916(3) Å, c = 7.107(1) Å, V = 1559.1(4) Å 3 (Zlatá Idka) and a = 15.985(1) Å, c = 7.154(1) Å, V = 1583.1(2) Å 3 (Přibyslavice). The composition (average of 5 electron microprobe analyses from Zlatá Idka and 5 from Přibyslavice) is (in wt%): SiO 2 33.85 (34.57), TiO 2 <0.05 (0.72), Al 2 O 3 39.08 (33.55), Fe 2 O 3 not determined (0.61), FeO 11.59 (13.07), MnO <0.06 (0.10), MgO 0.04 (0.74), CaO 0.30 (0.09), Na 2 O 1.67 (1.76), K 2 O <0.02 (0.03), F 0.26 (0.56), Cl 0.01 (<0.01), B 2 O 3 (calc.) 10.39 (10.11), H 2 O (from the crystal-structure refinement) 2.92 (2.72), sum 99.29 (98.41) for Zlatá Idka and Přibyslavice (in parentheses). A combination of EMPA, Mössbauer spectroscopy, and crystal-structure refinement yields empirical formulas (Na 0.591 Ca 0.103 □ 0.306 ) Σ1.000 (Al 1.885 Fe 2+ 1.108 Mn 0.005 Ti 0.002 ) Σ3.000 (Al 5.428 Mg 0.572 ) Σ6.000 (Si 5.506 Al 0.494 ) Σ6.000 O 18 (BO 3 ) 3 (OH) 3 (O 0.625 OH 0.236 F 0.136 Cl 0.003 ) Σ1.000 for Zlatá Idka, and (Na 0.586 Ca 0.017 K 0.006 □ 0.391 ) Σ1.000 (Fe 2+ 1.879 Mn 0.015 Al 1.013 Ti 0.093 ) Σ3.00 (Al 5.732 Mg 0.190 Fe 3+ 0.078 ) Σ6.000 (Si 5.944 Al 0.056 ) Σ6.000 O 18 (BO 3 ) 3 (OH) 3 (O 0.579 F 0.307 OH 0.115 ) Σ1000 for Přibyslavice. Oxy-schorl is derived from schorl end-member by the AlOFe -1 (OH) -1 substitution. The studied crystals of oxy-schorl represent two distinct ordering mechanisms: disorder of R 2+ and R 3+ cations in octahedral sites and all O ordered in the W site (Zlatá Idka), and R 2+ and R 3+ cations ordered in the Y and Z sites and O disordered in the V and W sites (Přibyslavice).

Three samples of the skarn mineral rustumite Ca 10 (Si 2 O 7 ) 2 (SiO 4 )(OH) 2 Cl 2 , space group C2/c, a ≈7.6, b ≈ 18.5, c ≈ 15.5 Å, β ≈ 104°, with variable OH, Cl, F content were investigated by electron microprobe, single-crystal X-ray structure refinements, and Raman spectroscopy. “Rust1_LCl” is a low chlorine rustumite Ca 10 (Si 2 O 7 ) 2 (SiO 4 )(OH 1.88 F 0.12 )(Cl 1.28 ,OH 0.72 ) from skarns associated with the Rize batholith near Ikizedere, Turkey. “Rust2_F” is a F-bearing rustumite Ca 10 (Si 2 O 7 ) 2 (SiO 4 )(OH 1.13 F 0.87 ) (Cl 1.96 OH 0.04 ) from xenoliths in ignimbrites of the Upper Chegem Caldera, Northern Caucasus, Russia. “Rust3_LCl_F” represents a low-Cl, F-bearing rustumite Ca 10 (Si 2 O 7 ) 2 [(SiO 4 ) 0.87 (H 4 O 4 ) 0.13 ](OH 1.01 F 0.99 ) (Cl 1.00 OH 1.00 ) from altered merwinite skarns of the Birkhin massif, Baikal Lake area, Eastern Siberia, Russia. Rustumite from Birkhin massif is characterized by a significant hydrogarnet-like or fluorine substitution at the apices of the orthosilicate group, leading to specific atomic displacements. The crystal structures including hydrogen positions have been refined from single-crystal X-ray data to R1 = 0.0205 (Rust1_LCl), R1 = 0.0295 (Rust2_F), and R1 = 0.0243 (Rust3_LCl_F), respectively. Depletion in Cl and replacement by OH is associated with smaller unit-cell dimensions. The substitution of OH by F leads to shorter hydrogen bonds O-H···F instead of O-H···OH. Raman spectra for all samples have been measured and confirm slight strengthening of the hydrogen bonds with uptake of F. This study discusses the complex crystal chemistry of the skarn mineral rustumite and may provide a wider understanding of the chemical reactions related to contact metamorphism of limestones

“Vanadium-dravite” NaMg 3 V 6 (Si 6 O 18 )(BO 3 ) 3 (OH) 3 OH (IMA number 1999-050) has been redefined as oxy-vanadium-dravite with end-member formula NaV 3 (V 4 Mg 2 )Si 6 O 18 (BO 3 ) 3 (OH) 3 O. The new name and the new formula have been approved by the CNMNC (IMA proposal 11-E). Oxy-vanadium-dravite occurs in the metamorphic rocks of the Sludyanka complex (southern Baikal region, Russia). The crystal structure of oxy-vanadium-dravite has been refined for the first time using single-crystal X-ray data, with a statistical index R1 for all reflections converging to 1.44%. The structure is rhombohedral, space group R3m, with the unit-cell parameters a = 16.1908(4), c = 7.4143(2) Å, V = 1683.21(7) Å 3 , Z = 3. The chemical characterization resulted in the empirical structural formula: X (Na 0.88 K 0.07 □ 0.05 ) Y (V 3+ 2.46 Mg 0.48 Ti 0.06 ) Z (V 3+ 3.14 Mg 1.74 Al 0.91 Cr 3+ 0.21 ) T (Si 5.99 Al 0.01 O 18 ) B (BO 3 ) 3 V (OH) 3 W (O 0.78 OH 0.14 F 0.08 ). Ideally, the oxy-vanadium-dravite is related to oxy-dravite and oxy-chromium-dravite by the homovalent substitution V 3+ → Al and V 3+ → Cr 3+ (respectively) at the Y and Z sites. The occurrence of solid-solutions among V 3+ , Cr 3+ , and Al have been observed in tourmalines from metamorphic rocks of the Sludyanka complex. Significant chemical variations in V 3+ , Cr 3+ , and Al were also observed within zoned crystals from Sludyanka, not belonging to the holotype specimen.

Fuettererite, Pb 3 Cu 6 2+ Te 6+ O 6 (OH) 7 Cl 5 , is a new tellurate from Otto Mountain near Baker, California, named for Otto Fuetterer who is largely responsible for the development of the mining claims on Otto Mountain. The new mineral is known from only two specimens, one from the NE2 vein and the other from the Bird Nest drift. Fuettererite occurs in vugs in quartz, on the first specimen associated with Br-rich chlorargyrite, iodargyrite, and telluroperite and on the second specimen associated with anglesite, anatacamite, atacamite, chalcopyrite, galena, goethite, hematite, muscovite, phosphohedyphane, timroseite, and wulfenite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Fuettererite is hexagonal, with space group R3̄, a = 8.4035(12), c = 44.681(4) Å, V = 2732.6(6) Å 3 , and Z = 6. Crystals are tabular to short prismatic, exhibit the forms {100}, {101}, and {001} and reach a maximum dimension of 50 μm. The color is bluish green, the streak is pale bluish-green, and the luster is adamantine. The Mohs hardness is estimated at between 2 and 3. The new mineral is brittle with irregular fracture and one perfect cleavage on {001}. The calculated density based on the empirical formula is 5.528 g/ cm 3 . Fuettererite is uniaxial (-), with calculated indices of refraction of ω = 2.04 and ε = 1.97, and is dichroic bluish-green, E < O. Electron microprobe analysis provided: PbO 41.45, CuO 30.35, Al 2 O 3 0.23, TeO 3 12.80, Cl 12.08, H 2 O 3.55 (structure), O=Cl -2.73, total 97.73 wt%. The empirical formula (based on 18 O + Cl apfu) is: Pb 2.88 Cu 2+ 5.92 Al 0.07 Te 6+ 1.13 O 6.59 (OH) 6.12 Cl 5.29 . The ten strongest powder X-ray diffraction lines are [d obs in Å (hkl) I]: 6.106 (104) 44, 3.733 (0.0.12) 100, 2.749 (121̄) 53, 2.6686 (124̄) 49, 2.5289 (127̄) 41, 2.2772 (1.2.11) 38, 1.9637 (315, 1.2.1̄6̅) 87, 1.8999 (multiple) 48, 1.5976 (multiple) 40, and 1.5843 (410, 1.2.23, 143) 44. The crystal structure of fuettererite (R 1 = 0.031 for 971 reflections with Fo > 4σF) contains edge-sharing sheets of CuO 5 Cl and TeO 6 octahedra. These sheets are virtually identical to that in the structure of spangolite, but in fuettererite they are linked together to form a double sheet. The double octahedral sheets alternate with thick double layers of PbO 2 Cl 6 polyhedra. The CuO 5 Cl octahedra exhibit pronounced Jahn-Teller distortions and the PbO 2 Cl 6 polyhedron has a lopsided distribution of bond lengths attributable to the localization of the Pb 2+ 6s 2 lone-pair electrons.

Agaite, Pb 3 Cu 2+ Te 6+ O 5 (OH) 2 (CO 3 ), is a new tellurate from the Aga mine on Otto Mountain near Baker, California, U.S.A. The new mineral is known from only one specimen. It occurs on quartz in association with cerussite, Br-rich chlorargyrite, chrysocolla, goethite, khinite, markcooperite, muscovite, phosphohedyphane, timroseite, and wulfenite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Agaite is orthorhombic, space group Pca2 1 , with unit-cell dimensions a = 10.6522(7), b = 9.1630(5), c = 9.6011(7) Å, V = 937.12(11) Å 3 , and Z = 4. Agaite crystals form as blades flattened on {010} and probably elongated on [001], and are up to about 20 μm thick and 200 μm in length. The color is blue, the streak is pale blue, and the luster is adamantine. The Mohs hardness is estimated at between 2 and 3. Agaite is brittle with an irregular fracture and one perfect cleavage on {010}. The calculated density based on the empirical formula is 6.987 g/cm 3 . Agaite is biaxial (-), with calculated indices of refraction of α = 2.015, β = 2.065, and γ = 2.070°. The measured 2V is 34(5)° and the optical orientation is X = b, Y = c, and Z = a. It is pleochroic: X = pale blue, Y and Z = blue; X < Y = Z. Electron microprobe analyses (average of 4) provided: PbO 65.91, CuO 7.75, TeO 3 17.41, CO 2 4.33 (structure), H 2 O 1.78 (structure), total 97.18 wt%. The empirical formula (based on 10 O apfu) is: Pb 3.00 Cu 2+ 0.99 Te 6+ 1.01 O 5 (OH) 2 (CO 3 ). The eight strongest powder X-ray diffraction lines are [d obs in Å (hkl) I]: 4.26 (012) 28, 4.165 (211) 14, 3.303 (022, 310, 221) 100, 2.7472 (131, 203, 312) 68, 2.571 (032, 401, 231) 14, 2.0814 (332, 422) 21, 2.0306 (511) 17, and 1.7468 (multiple) 40. The crystal structure of agaite (R 1 = 0.033 for 1913 reflections with Fo > 4σF) contains edge-sharing chains of Cu 2+ O 5 square pyramids and Te 6+ O 6 octahedra parallel to a that are joined by corner-sharing in the c direction, forming a polyhedral sheet parallel to {010}. The polyhedral sheet is very similar to those in the structures of timroseite and paratimroseite. The thick interlayer region contains 8- and 9-coordinated Pb2+, as well as CO 3 and OH groups. The Pb coordinations have lopsided distributions of bond lengths attributable to the localization of the Pb 2+ 6s 2 lone-pair electrons.

The occurrence of vorlanite, cubic CaUO 4 , is reported in the Nopal I uranium deposit (Sierra Peña Blanca, Mexico). This is the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Vorlanite occurs as nanoscale crystals embedded in U-bearing opal, with a Ca/U ratio of ~1. Association with opal suggests that vorlanite formed at Nopal during late-stage U-mobilization under oxidizing conditions and low (<50 °C) temperature. The presence of nanoscale uranate crystals in an environment largely dominated by uranyl silicates indicates that uranates may play a role in uranium scavenging at low temperature. In addition, the occurrence of vorlanite in the crystal shape consistent with its structure provides unique information on its conditions of formation.