The high-temperature phase equilibrium relationships in the system diopside-anorthite—åkermanite have been investigated by the quenching method. This system may be regarded as essentially a simple eutectic system. The eutectic is located at the composition 9 diopside:44 anorthite:47 åkermanite (by weight) and at a temperature of 1226° C. Åkermanite is a stable phase at least as low as this temperature. Triclinic anorthite is the only form of CaAl2Si2O8 encountered in the liquidus range of temperatures.

Zolotarevite (IMA2020-076), ideally Na5Zr[Si6O15(ОН)3]⋅2–3H2O, is а new mineral of the lovozerite group. The mineral was found in a leucocratic nepheline syenite from Kedykverpakhk Mt., Lovozero alkaline massif, Kola Peninsula, Russia. It occurs as anhedral grains up to 1 mm across and is associated with microcline–perthite, nepheline, sodalite, aegirine, lamprophyllite, lueshite, umbozerite, lomonosovite, nastrophite, a mineral of the kazakovite–tisinalite series, sphalerite and löllingite. Zolotarevite is cherry red, with a vitreous lustre and white streak. The mineral is brittle, with a Mohs hardness of 5. Cleavage was not observed; the fracture is uneven. The measured density is 2.75(5) g⋅cm–3, the density calculated using the empirical formula and single-crystal unit-cell parameters is 2.85 g⋅cm–3. Zolotarevite is anomalously biaxial (–), α = 1.580(2), β = 1.600(2) and γ = 1.602(2) (for λ = 589 nm); 2Vmeas < 10°. Chemical data (electron microprobe, wt.%) are: Na2O 20.41, СаО 0.42, MnO 3.49, Fе2O3 0.55, SiO2 52.46, ТiO2 1.34, ZrO2 11.33, H2O (calculated from the structural formula) 10.20, total 100.20. The empirical formula based оn 6 Si atoms per formula unit is Na4.53Zr0.63Mn0.34Ti0.11Ca0.05Fe3+0.05Si6O14.43(ОН)3.56(H2О)2.11. Zolotarevite is trigonal, space group R${\bar 3}$m, with a = 10.294(6) Å, c = 13.115(8) Å, V = 1203.7(16) Å3 and Z = 3. The crystal structure was solved from single-crystal data and refined to R1 = 0.049. The strongest lines of the powder X-ray diffraction pattern [d in Å (I) (hkl)] are: 7.37 (69) (101); 5.26 (56) (012); 3.686 (64) (202); 3.330 (79) (113); 3.265 (99) (211), 2.640 (100) (024) and 2.576 (60) (220). Zolotarevite is unique in that it is a highly hydrated lovozerite-group mineral with the B site occupied by variable amounts of H2O.

Two metamorphic alteration styles have been observed in basic lavas and volcaniclastic rocks of the Builth Volcanic Series of Ordovician age exposed at Llanelwedd Quarry, in the Builth lnlier, Wales. The first alteration style is characterized by the development of a mineral assemblage comprising albite+chlorite+ sphene+ pumpellyite ± prehnite ± calcite ± white mica, although original textures are largely preserved. This alteration pattern corresponds with that developed in volcanic and volcaniclastic rocks elsewhere in Wales, and which is attributed to the effects of burial. The second alteration style is characterized by the development of metadomains dominated by pumpellyite or, more rarely, prehnite. In the metadomains no original textures are seen in hand specimen. This alteration pattern has, so far, not been observed elsewhere in Wales, and it is here suggested that it might result from a submarine hydrothermal circulation system.

The uncommon sodium rare-earth phosphate mineral vitusite-(Ce) (Na3RE(PO4)2) can be considered as the extreme product of sodium and rare-earth substitution in the apatite structure. Lesser amounts of substitution provide sodium and rare-earth-bearing apatites up to about 80 mol.% exchange; beyond this point vitusite is the stable phase. The structure of vitusite, determined previously from a synthetic analogue, can also be considered as a derivative from apatite, but with cations exchanged on sites normally occupied by anions. Vitusite can therefore be considered as a sodium- and rare-earthrich apatite end-member, with a distinct, but apatite-derived, structure, formed in highly persodic and high rare-earth environments. From an examination of the literature on diffusion in apatite, vitusite in principle could be formed from apatite sensu stricto by subsolidus diffusion in response to late-stage Naand RE-rich hydrothermal fluids.

The petrography and geochemistry of a suite of dolerite dykes emplaced into orthogneisses of the Jotun Nappe, central southern Norway, are described. The dolerites, which appear to be tholeiitic in character, show well-developed ophitic and doleritic textures and are not foliated. They contain corona structures of six types which represent the various stages of reaction between olivine or clinopyroxene and plagioclase, and oxide grains and plagioclase. Corona growth always proceeds after the plagioclase has become clouded with numerous extremely fine opaque particles, and reaches its fullest development in rocks with the most heavily clouded plagioclase. Garnet grows in coronas only in rocks with Fe2O3/(Fe2O3 + FeO) = 0.20 to 0.27. The ratio MgO/MgO + Fe2O3 + FeO) is of lesser importance in controlling the growth of this mineral. The role of water in coronaforming reactions, and the preservation of original igneous textures indicates that the coronas are a product of post-solidification deuterism, possibly active at high pressures and temperatures, rather than of prograde metamorphism.

The new minerals cuatrocapaite-(NH4) (IMA2018-083) and cuatrocapaite-(K) (IMA2018-084) are the NH4- and K-dominant members of a series with the general formula (NH4,K)3(NaMg□)(As2O3)6Cl6·16H2O. Both minerals were found at the Torrecillas mine, Iquique Province, Chile, where they occur as secondary alteration phases. Both minerals occur as hexagonal tablets up to ~0.3 mm in diameter. They are transparent, with a vitreous lustre and white streak. For both, the Mohs hardness is ca. 2½, the crystals are somewhat flexible, but not elastic, the fracture is irregular and the cleavage is perfect on {001}. The measured densities are 2.65(2) and 2.76(2) g/cm3 for the NH4- and K-dominant species, respectively. Optically, cuatrocapaite-(NH4) is uniaxial (–) with ω = 1.779(3) and ε = 1.541(3) and cuatrocapaite-(K) is uniaxial (–) with ω = 1.777(3) and ε = 1.539(3) (white light). The minerals are insoluble in acids, but decompose in NaOH(aq). The empirical formulas, determined from electron-microprobe analyses, are (NH4)2.48Na1.66Mg0.87K0.09(As12O18.05)Cl5.88·16.02H2O and K2.68Na1.33Mg0.93(NH4)0.31(As12O18.01)Cl6.16·16.04H2O. The minerals are trigonal, space group R${\bar 3}$m; the cuatrocapaite-(NH4) cell parameters are a = 5.25321(19), c = 46.6882(19) Å, V = 1115.80(9) Å3 and Z = 1; the cuatrocapaite-(K) cell parameters are a = 5.2637(15), c = 46.228(8) Å, V = 1109.2(7) Å3 and Z = 1. The structures, refined for cuatrocapaite-(NH4) to R1 = 1.78% for 544 Io > 2σI reflections, contain four types of layers: (1) a planar neutral As2O3 (arsenite) sheet; (2) an (${\rm NH}_{\rm 4}^{\vskip -2pt\rm \scale65% +} $,K+) layer that links adjacent arsenite sheets; (3) a Cl– layer placed on the As side of each arsenite; and (4) a layer containing partially occupied Na, Mg and H2O sites that is flanked on either side by Cl layers. The layer sequence for the type 1, 2 and 3 layers is identical to the Cl–As2O3–K–As2O3–Cl layer sequence in the structures of lucabindiite and gajardoite.

Orbicules in diorite from the Grenville Front zone of eastern Labrador consist of biotite- and/or hornblende-studded, dioritic cores enclosed by fine-grained shell structures alternately enriched and depleted in biotite. The orbicules occur in a mesocratic, quartz-bearing matrix. Epidote of inferred magmatic origin occurs in all parts of the rock. Plagioclase in the matrix is relatively sodic, and biotite more ferroan than in the orbicules, suggesting that the matrix material has the most evolved composition, and crystallized last.

The diorite is unusually aluminous (orbicules: 24.9-27.4 wt.% Al2O3; matrix: 22.4-23.6% Al2O3) and calcic (orbicules: 7.0-8.4 wt.% CaO; matrix: 6.0-6.9% CaO); it shows a positive Eu anomaly, and has elevated Sr concentrations (1800-2500 ppm Sr), demonstrating that, compositionally, it resembles a plagioclase cumulate. Mass-balance calculations suggest that the orbicule cores had a crystal/melt ratio of ≤5. This accounts for the extreme fractionation of the rock (e.g., in orbicules, Zr <5 ppm). Compared with fractional crystallization patterns, variation diagrams show counter-trends (e.g. the siliceous matrix contains elevated TiO2) or scatter for several components, suggesting that the crystal/melt ratio governed some of the geochemical characteristics of the diorite.

The presence of coarse mafic clots containing primary epidote, biotite and/or hornblende testify to an elevated water content in the orbieule cores. The shell magma apparently formed as a result of the interaction of supercooled orbicule core fluids with the matrix magma, and tended to serve as a reservoir for alkalis and Fe. Alkalis and Ca diffused in opposite directions, possibly as a result of a temperature gradient at the orbicule/matrix interface. This, however, requires decoupling of the thermodiffusional behaviour of alkalis and femic components in hydrated intermediate magma, which contrasts with documented Soret diffusion in mafic systems.

The solidification of the shell magma prior, to the orbicule cores and matrix is attributed to dewatering, consistent with the fine grain size of the shell structures. Except where remobilized core material has disrupted the shells, the cores crystallized in isolation from the matrix, which fractionated toward a more evolved composition.

Advances in the design of environmental reaction cells and in the collection of X-ray diffraction data are transforming our ability to study mineral-fluid interactions. The resulting increase in time resolution now allows for the determination of rate laws for mineral reactions that are coupled to atomic-scale changes in crystal structure. Here we address the extension of time-resolved synchrotron diffraction techniques to four areas of critical importance to the cycling of metals in soils: (1) cation exchange; (2) biomineralization; (3) stable isotope fractionation during redox reactions; and (4) nucleation and growth of nanoscale oxyhydroxides.

The systematics of cation ordering in binary spinel solid solutions have been investigated using an interatomic potential model combined with Monte Carlo simulations. The formalism to describe a system containing three cation species ordering over two non-equivalent sub-lattices is developed and the method applied to the MgAl2O4-FeAl2O4 binary solid solution. Our results compare favourably with experimental measurements of site-occupancy data, although the experiments display a slightly larger degree of non-ideality than the simulations. A possible kinetic origin of the non-ideal behaviour was examined by performing simulations in which only exchange of Mg and Fe2+ between tetrahedral and octahedral sites was permitted below the Al-blocking temperature of 1160 K. This approach improves the agreement with the experimental site occupancies, and suggests that the blocking temperature for moving Mg and Fe2+ between tetrahedral and octahedral sites is significantly lower than for moving Al

Dwornikite, (Ni1−xFex)SO4 · H2O is a member of the kieserite group, monoclinic with space group C2/c. Specimens from Minasragra, Peru with x ∼ 0.1 have a unit cell with a = 6.839(2), b = 7.582(2), c = 7.474(2) Å, and β = 117.85(2)°. The six strongest lines of the powder pattern are: 3.342 (12, 100), 4.732 (110, 70), 3.024 (200, 70), 4.754 (11, 50), 3.293 (021, 35), 2.491 (022, 35). The mineral occurs as fine grained white aggregates associated with vanadium sulphide ores containing patronite and bravoite, mixed with other oxidation products. New unit cell data for the synthetic end-member compounds NiSO4 · H2O and FeSO4 · H2O, and new X-ray powder data for retgersite (NiSO4 · 6H2O) are provided.

Fluids trapped inside fluid inclusions in quartz from the multiphase Starav monzogranite in Etive, Argyll, were extracted under vacuum and quantitative data for H2O and CO2 were obtained manometrically. Na and K were determined on an aqueous leach from the decrepitated grains. A bivariate diagram of H2O/CO2 versus Na/K discriminates between magma pulses and mirrors the whole-rock trace-element chemistry. This work shows that compositional variations of fluids in quartz from a weakly mineralised granitoid intrusion are sensitive indicators of its magmatic history and identify subtle changes in its mineralogical composition.

1666 moldavites from 19 localities in Bohemia and 617 moldavites from 10 localities in Moravia were measured to yield parameters L (length), B (breadth), and T (thickness). A digital computer was programmed to calculate values T/L, (L-B)/(L-T), and according to Sneed and Folk (1958) and values q = B/L, p = T/B, and F = p/q according to Zingg (1935). Averages of large numbers of values characterize Bohemian and Moravian localities. Moldavites from most localities in Bohemia are often drop-like, flat or elongate with average values of between 0·53 and 0·66 and F between 0·68 and 0·91. Moldavites from Moravia are frequently massive to spheroidal with average in the range 0·60 to 0·75 and F between 0·87 and 1·08. Among the localities in Bohemia, four have moldavites with morphological features of Moravian moldavites. The data obtained permit an interpretation that localities of moldavites with low average sphericity contain less heated material. Less heated and thus more viscous glass could have flown along shorter trajectories (Bohemia). More heated glass was ejected to geographically more distant places (Moravia) or travelled along relatively long steeper trajectories (several localities in Bohemia).

After approximately 50% of K from the 1–2 μm fraction of a naturally occurring microcrystalline muscovite was extracted with BaCl2 solution at 98°C electron-diffraction patterns showed a honeycomb-shaped diffuse scattering as well as intense diffuse streaks. The diffuse scattering became pronounced with increasing K-depletion. It may be interpreted in terms of a short-range order distribution of interlayer Ba ions, using an analogy to the work by Alcover et al. (1972, 1976). Since the diffuse streaks still remained after re-entry of K to the K-depleted specimen they might be related to structural disturbance, particularly in the basal oxygen arrangements, resulting from the K-extraction. Subsequent conversions of Ba-saturated vermiculitized muscovite into Na-, Mg-, and Ca-forms revealed distinct extra diffraction spots midway between two ordinary diffraction spots. They were broader than the ordinary spots and elongated along the three directions of [01]*, [11]*, and [11]*. The diffraction pattern containing the extra spots was, therefore, interpreted as a composite one made up by superimposing three independent patterns, each of which was composed of ordinary Bragg diffraction spots and extra diffraction maxima elongated in one of the three directions. This situation does not require a superlattice but modified the original face-centred lattice symmetry to a primitive lattice symmetry. However, the presence of a real superlattice should also be possible. The elongation and broadness of the extra diffraction maxima may be related to the orientation and size of coherent domains defined by a certain ordering of interlayer cationic distribution, which took place during the hydration processes including extraction and conversion.

Experimental breakdown of staurolite + inclusions of albite and muscovite (representing an aluminous Fe-rich metapelitic composition) occurs within the KNFMASH system at 800°C and 0.1 GPa under fluid-present conditions over periods of 2 days to 8 weeks. The overall melt-producing reaction is staurolite + muscovite + plagioclase + vapour = hercynite + corundum + mullite + quartz + liquid, and involves three reactions; staurolite + vapour = hercynite + corundum + quartz + liquid, albite + vapour = mullite + liquid, and muscovite + vapour = mullite + liquid. Melt (glass) compositions are siliceous (77.2–64.5 wt.% SiO2), peraluminous (A/CNK = 1.5–5.5), and have granite-trondjhemite compositions in terms of normative Ab-Ab-Or contents. Textures indicate that quartz formed later than corundum. The corundum + quartz + hercynite assemblage after staurolite is considered to be metastable and only likely to be found in nature where staurolite-bearing rocks have undergone rapid heating and melting followed by quenching.

Bassoite, ideally SrV3O7·4H2O, is a new mineral from the Molinello manganese mine, Val Graveglia. eastern Liguria, northern Apennines, Italy. It occurs as black euhedral to subhedral grains up to 400 urn across, closely associated with rhodonite, quartz and braunite. Bassoite is opaque with a sub-metallic lustre and a black streak. It is brittle and neither fracture nor cleavage was observed; the Vickers micro-hardness (VHN100) is 150 kg/mm (range 142—165; corresponding to a Mohs hardness of 4—41/2). The calculated density is 2.940 g/cm3 (on the basis of the empirical formula and X-ray single-crystal data). Bassoite is weakly bireflectant and very weakly pleochroic from grey to a dark green. Internal reflections are absent. The mineral is anisotropic, without characteristic rotation tints. Reflectance percentages (Rmin and Rmax) for the four standard COM wavelengths are 18.5%, 19.0% (471.1 nm); 17.2%, 17.8% (548.3 nm); 16.8%, 17.5% (586.6 nm) and 16.2%, 16.8% (652.3 nm), respectively.

Bassoite is monoclinic, space group P21/m, with unit-cell parameters: a = 5.313(3) Å, b = 10.495(3) Å, c = 8.568(4) Å, β = 91.14(5)°, V= 477.7(4) Å3, a:b:c = 0.506:1:0.816, and Z = 2. The crystal structure was refined to R1 = 0.0209 for 1148 reflections with Fo > 4σ(Fo) and it consists of layers of VO5 pyramids (with vanadium in the tetravalent state) pointing up and down alternately with Sr between the layers (in nine-fold coordination). The nine most intense X-ray powder-diffraction lines [d in Å (I/I0) (hkt)] are: 8.5663 (100) (001); 6.6363 (14) (011); 3.4399 (14) (1̄21); 3.4049 (17) (121); 2.8339 (15) (1̄22); 2.7949 (11) (122); 2.6550 (15) (200); 2.6237 (11) (040) and 1.8666 (15) (240). Electron microprobe analyses produce a chemical formula (Sr0.97Ca0.02Na0.01)V3.00O74H20, on the basis of 2(Sr+Ca+Na) = 1, taking the results of the structure refinement into account. The presence of water molecules was confirmed by micro-Raman spectroscopy. The name honours Riccardo Basso (b. 1947), full professor of Mineralogy and Crystallography at the University of Genova. The new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2011-028).

An investigation of the relative stabilities and equations of state of possible Fe3S polymorphs was conducted using first-principles pseudopotential calculations. These calculations were based on density functional theory and performed using ultrasoft Vanderbilt pseudopotentials within the generalized gradient approximation. In accord with experiment, we found that the tetragonal Fe3P-type polymorph is the only stable phase along the 0 K isotherm as a function of pressure. Fe3S exhibits permanent magnetism at ambient conditions (Fei et al., 2000), but magnetism is suppressed by pressure and temperature, and therefore non-magnetic data are appropriate ones to use for modelling planetary interiors. For this reason, and because the Fe3P-type polymorph of Fe3S contains 32 atoms per unit cell it was impractical to incorporate magnetic properties into the simulations of this phase, we studied the behaviour of the non-magnetic phase. We obtained values of 250 GPa for the bulk modulus, K0, and 4.61 for its first derivative withrespect to pressure, K0′, by fitting a 3rd order Birch-Murnaghan equation of state to the calculated internal energy as a function of volume for the non-magnetic Fe3P-type Fe3S. This suggests that a pressure far greater than that expected in the Martian interior would be needed to achieve a density comparable to that of the Martian core. We therefore conclude that it is unlikely that the core of Mars contains significant amounts of solid Fe3S.

Oscarkempffite, ideally Ag10Pb4(Sb17Bi9)∑=26S48, is a new mineral species found in old material (1929–30) from the Colorada vein, Animas mine, Chocaya Province, Department of Potosi, Bolivia. It is associated with aramayoite, stannite, miargyrite, pyrargyrite and tetrahedrite. Oscarkempffite forms anhedral grains and grain aggregates up to 10 mm across. The mineral is opaque, greyish black with a metallic lustre; it is brittle without any discernible cleavage. In reflected light oscarkempffite is greyish white, pleochroism is distinct, white to dark grey. Internal reflections are absent. In crossed polars, anisotropism is distinct with rotation tints in shades of grey. The reflectance data (%, air) are: 39.9, 42.6 at 470 nm, 38.6, 41.7 at 546 nm, 38.1, 41.2 at 589 nm and 37.3, 40.6 at 650 nm. Mohs hardness is 3–3½, microhardness VHN50 exhibits a range 189–208, with a mean value 200 kg mm–2. The average results of four electron-microprobe analyses in a grain are: Cu 0.24(7), Ag 14.50(8), Pb 11.16(14), Sb 28.72(16), Bi 24.56(17), S 20.87(5), total 100.05(6) wt.%, corresponding to Cu0.24Ag9.92Pb4.00Sb17.36Bi8.64S47.84 (on the basis of Me + S = 88 apfu). The simplified formula, Ag10Pb4Sb17Bi9S48, is in accordance with the results of a crystal-structure determination. The density, 5.8 g cm–3, was calculated using the ideal formula. Oscarkempffite has an orthorhombic cell with a = 13.199(2), b = 19.332(3), c = 8.249(1) Å, V = 2116.3(5) Å3, space group Pnca and Z = 1. The strongest eight lines in the (calculated) powder-diffraction pattern are [d in Å(I)hkl]: 3.66(35)(122), 3.37(70)(132), 3.34(100)(250), 2.982(55)(312), 2.881(86)(322), 2.733(29)(332), 2.073(27)(004) and 2.062(31)(182). Comparison with gustavite, andorite and roshchinite confirms its independence as a mineral species.