Band 99, Heft 4

New data based on a detailed analysis of pyroxene zoning strongly suggests that convection is an important process in lunar magmas. Elardo and Shearer (2014) carefully document irregular oscillatory zoning that is best explained by movement of pyroxene crystals in a convecting magma. Lunar samples that contain such data are rare, but this study should inspire more extensive efforts to further document magmatic processes.

In a recent of issue American Mineralogist , Rollin-Martinet et al. (2013, vol. 98, p. 2037- 2045) take a thermodynamic, in contrast to a medical- biological, approach to the maturation process of biological apatite. They do so by focusing on changes in the HPO 4 2- concentration in biomimetic apatite over time. In this first-of-its-kind analysis, they conclude that the increase in stability of bone mineral over time ultimately demands that bone be remodeled (i.e., replaced by new bone) in order for the mineral to retain its biologically important functional properties.

Combining new measurements of thermal diffusivity (D) and viscosity (η) of 13 silica-rich glasses and their melts with previous data reveals specific effects of Al, Ca, and Fe cations on heat and mass transport for diverse glasses and melts. We investigated rhyolites, tektites, leucogranite, haplogranite, and chemically complex commercial glasses. Highly polymerized samples, with high-Al but low-Ca contents, yield high values for η, D, and glass transition temperatures (T g,12 ), whereas less polymerized samples with high-Ca but low-Al contents, have low η, D, and T g,12 . Upon crossing the glass transition, D decreases substantially, to ~ 0.35 mm 2 /s for Ca-rich melts, but D decreases only weakly, to ~ 0.52 mm2/s for Al-rich melts. The magnitude of the decrease in D at T g,12 correlates with the melt fragility, and also to the configurational heat capacity. High-Ca contents result in low D for glasses and melts, whether or not Al is present. At high T, ∂D/∂T is positive for glasses and melts containing Fe 2+ , which we attribute to diffusive radiative transfer involving electronic-vibronic coupling. Thermal conductivity of all glasses increases with T, flattening out as the transition is approached. For melts with >1 wt% FeO total , ∂k/∂T is positive. We predict that upon melting, I-type arc granite liquids should have lower thermal diffusivity than calcium-poor A- or S-types, and calc-alkaline basalts will have lower D than tholeiitic basalts, such that D of granitic melts is ~ 0.2 mm 2 s -2 higher than basaltic. Ferrous iron enhancing heat transport could alter the predicted order at higher temperatures.

Speciation of D-O-H-C-N volatiles in alkali aluminosilicate melts and of silicate in D-O-H-C-N fluid has been determined in situ to 800 °C and >2 GPa under reducing and oxidizing conditions by using an externally heated hydrothermal diamond-anvil cell with Raman spectroscopy as the structural probe. Reducing conditions were near those of the IW oxygen buffer, whereas oxidizing conditions were obtained by conducting the experiments with oxidized components only and with Pt as a catalyst. Raman bands assigned to C-H stretching in CH x D y isotopologues and CH 4 groups (including CH 3 ) were employed to determine the CH 4 /CH x D y ratio in fluids and melts. This ratio decreases from 1.5-2 at 500 °C to between 1.2 and 1 with 800 °C with Δ H -values of 13.6 ± 2.1 and 5.5 ± 1.1 kJ/mol for melt and fluid, respectively. The CH 4 /CH x D y fluid/melt partition coefficient ranges between ~ 16 and ~ 3 with Δ H = 33 ± 6 kJ/mol assuming no pressure effect. This behavior of deuterated and protonated complexes is ascribed to speciation of volatile and silicate components in fluids and melts in a manner that is conceptually similar to D/H partitioning among complexes and phases in brines and hydrous silicate systems. Molecular N 2 is the N-bearing species in fluids and melts under oxidizing conditions. Under reducing conditions, the dominant species are molecular NH 3 and ammine groups, NH 2 - . The NH 3 / NH 2 ratio varies between 0.15 and 0.75 in the 425-800 °C temperature range. The enthalpy change of the ammonia/ammine equilibrium, Δ H , derived from the temperature and assuming no pressure effect on the equilibrium, is 19 ± 8 and 61 ± 9 kJ/mol for melt and fluid, respectively. The fluid/melt partition coefficient, (NH 3 + NH 2 - ) fluid /(NH 3 + NH 2 - ) melt , ranges from 8 to 3 with Δ H = 45 ± 12 kJ/mol. For oxidized nitrogen, the fluid/melt partition coefficient is twice or more of those values for reduced nitrogen. Hydrogen bonding can be detected at 500 °C and below. This behavior resembles that of H 2 O. Deuterium-containing analogues of the (N+H)-species could not be detected with precision because these were in the frequency-range of the second-order Raman shift of diamond in the diamond-anvil cell itself and could not be isolated from the strong background generated by the Raman intensity from the diamond. These results imply that, unlike noble gases, degassing of N-bearing species from the mantle is redox dependent, and is also more efficient at lower temperatures (shallow depths). Reduced and oxidized C-O-H-N species exist fluids and melts in the modern mantle, whereas reduced species dominated in the young Earth. The f H2 -dependent speciation C-O-H-N volatile components result in f H2 -dependent thermodynamic and transport properties of fluids and melts in the interior of the Earth and terrestrial planets. In fluids, the solubility of nominally incompatible trace elements can increase by orders of magnitude upon its saturation with silicate components. Trace element and stable isotope partitioning between fluids and melt can change by >100% for the same reason.

The effect of pH on the kinetics of chrysotile dissolution was investigated at 25 °C in batch reactors over the pH range of 1 to 13.5, in oxalic solutions and buffered solutions of inorganic salts. Dissolution rates were obtained based on the release of Si and Mg. Results of the batch with inorganic buffers showed a strong dependence of dissolution rates on pH in the acid range. The logarithm of dissolution rates decreases with the pH with a slope of n = 0.27. Around neutral pH, a minimum is reached. From pH 8 to 12, rates increase again when pH increases, and follow a linear dependence with a shallow slope ( n = 0.06). The Mg/Si ratio shows a non-stoichiometric dissolution reaction with a preferential release of Mg 2+ at acidic pH; it decreases at neutral pH conditions according to Mg solubility. Our results suggest that the relative ease of the breaking of Mg-O bonds compared with Si-O bonds lead to dissolution via a series of steps involving Si and Mg, where Si release is the rate-limiting step. In the presence of 15 mmol L -1 oxalate, an intense catalytic effect from pH 1 to 6 is observed because of the capacity of the oxalate anion to form different complexes with Mg. The ratio of the rates derived from Mg and Si concentrations confirm an enhancement of non-stoichiometric dissolution compared with the series without oxalate. The mechanism of catalysis involves different processes depending on pH: At pH 1, XRD analysis confirms the formation of an amorphous silica phase dissolving all the Mg present in the chrysotile structure. At pH 2, XRD and FTIR results also confirm the precipitation of glushinskite, a magnesium oxalate phase. At pH 3 to 6, the presence of oxalate enhances dissolution almost by an order of magnitude compared with the experiments in inorganic buffered solutions. In this case, the mechanism could be due to the formation of aqueous or surface magnesium oxalate complexes. However, dissolution rates at neutral pH in the presence of oxalate are similar to those obtained in inorganic buffered solutions; the pH dependence at pH 8 to 13 is minimal. The increase in saturation and the drastic decrease in Mg solubility at these pH values could lead to precipitation of secondary phases coating the reactive mineral surface and inhibiting the surface. Results obtained in this study show that chrysotile dissolves faster in acid media and oxalate acts as a strong catalyst increasing the efficiency of magnesium release to solution at ambient temperature. These data may provide an excellent background to design and select optimal conditions in the previous acid treatment for carbon capture processes, as well as help to develop remediation process of asbestos contaminated sites.

Meteorite Northwest Africa (NWA) 6963 was classified as a basaltic shergottite based on mineralogy, but here we show that it is a gabbroic rock with a quartz-alkali feldspar intergrowth that represents a late-stage granitic melt. NWA 6963 contains clinopyroxene and maskelynite grains up to 5 mm in length, with minor ferroan olivine, spinel, ilmenite, merrillite, apatite, Fe-sulfides, and high-Si glass. NWA 6963 also contains areas of quartz and alkali-feldspar intergrowths up to ~ 1 mm in size. Based on mineral abundances and textural analysis, we suggest that NWA 6963 is an intrusive rock similar to a terrestrial gabbro. Infiltration of the martian crust by young gabbroic bodies would suggest that estimates of crustal composition, density, and thickness based on the surface chemistry alone would be problematic and the martian crust may be even more heterogenous than is seen from orbit alone. Investigations of crater walls, where intrusive crustal rocks would be exposed, are needed to discover the launch sites of the shergottites and the full heterogeneity of the martian crust.

Césarferreiraite, Fe 2+ Fe 2 3+ (AsO 4 ) 2 (OH) 2 ·8H 2 O, is a new laueite-group mineral (IMA 2012-099) of triclinic symmetry, from Eduardo pegmatite mine, Conselheiro Pena municipality, Minas Gerais, Brazil. Intimately associated minerals are pharmacosiderite, scorodite, and earlier arsenopyrite, and probably césarferreiraite replaces the latter. It occurs as fibrous-to-tabular aggregates up to 2 mm. Single crystals, up to 10 μm long with a thickness of about 1-2 μm, are elongated along [001] and flattened on (100). The fibers have almost rectangular cross-section apparently bound by the {100} and {010} pinacoid forms. Color and streak are pale to greenish yellow. Luster is vitreous; individual crystals are transparent and masses are translucent. Cleavage is distinct, presumably on {010} and {100}. Calculated density is 2.934 g/cm 3 . The mineral is biaxial (+), n (min) = 1.747(3), n (max) = 1.754(3) (589 nm). IR spectrum of césarferreiraite is unique and can be used for the identification of the mineral. Chemical composition ( n = 4, WDS, calculated for the condition Fe 2+ :Fe 3+ = 1:2, H 2 O for the ideal structural formula, wt%) is: FeO 11.50, Fe 2 O 3 25.56, CaO 15.41, As 2 O 5 33.51, H 2 O 26.01, total 100.12. The empirical formula (based on 18 O apfu) is Fe 2+ 0.98 Fe 3+ 1.96 [(AsO 4 ) 1.79 (PO 4 ) 0.31 ](OH) 1.52 ·8.08H 2 O. The strongest eight X-ray powder-diffraction lines [ d in Å( I )( hkl )] are: 9.85(95)(010), 6.35(100)(001), 3.671(29)(1̅21), 3.158(32)(13̅0), 2.960(39)(022̅), 2.884(35)(1̅31), 2.680(29)(2̅11), and 2.540(23)(2̅10). Unit-cell parameters refined from powder data indexed by analogy with related laueite-group minerals (space group: P 1̅) are: a = 5.383(2), b = 10.363(3), c = 6.878(2) Å, α = 96.42(4), β = 109.19(3), γ = 102.30(2)°, V = 347.1(2) Å 3 , and Z = 1. Gladstone-Dale compatibility is -0.020 (excellent). Césarferreiraite is the arsenate analog of ferrolaueite.

We studied the atomic structure and the chemical composition of (101)-type rutile (TiO2) twins from Diamantina in Brazil by electron microscopy methods to resolve the mechanism of their formation. The twin boundaries were studied in two perpendicular orientations to reveal their 3D structure. The presence of a precursor phase, such as Al-rich hydroxylian pseudorutile (HPR; kleberite), during the initial stages of the crystallization appears to be the necessary condition for the formation of (101) twins of rutile at this locality. The precursor with a tivanite-type structure serves as a substrate for the topotaxial crystallization of rutile. Depending on the initial crystallization pattern the rutile can grow either as a single crystal or as a twin. During the progressive crystallization of the rutile Al-rich oxyhydroxide (diaspore, α-Al 2 O 3 ) clusters are concentrated at the center of the precursor where they are pinned to the twin boundary as the precursor is fully recrystallized into rutile. At the increased temperatures the remaining diaspore precipitates are converted to corundum (α-Al2O3), while the two crystal domains continue to grow in the (101) twin orientation. In addition to the primary (101) twin, series of secondary {101} twins are formed to accommodate the residual tensile stress caused by the diaspore-to-corundum transformation. Based on the observed corundum-rutile [0001] C (112̄0) C ||[010] R (101) R and ilmeniterutile [0001] I (11̄00) I ||[010] R (301) R crystallographic relations a unified mechanism of the genesis of the {101} and {301} reticulated sagenite twin clusters is proposed.

Mathesiusite, K 5 (UO 2 ) 4 (SO 4 ) 4 (VO 5 )(H 2 O) 4 , a new uranyl vanadate-sulfate mineral from Jáchymov, Western Bohemia, Czech Republic, occurs on fractures of gangue associated with adolfpateraite, schoepite, čejkaite, zippeite, gypsum, and a new unnamed K-UO 2 -SO 4 mineral. It is a secondary mineral formed during post-mining processes. Mathesiusite is tetragonal, space group P 4/ n , with the unit-cell dimensions a = 14.9704(10), c = 6.8170(5) Å, V = 1527.78(18) Å 3 , and Z = 2. Acicular aggregates of mathesiusite consist of prismatic crystals up to ~ 200 μm long and several micrometers thick. It is yellowish green with a greenish white streak and vitreous luster. The Mohs hardness is ~ 2. Mathesiusite is brittle with an uneven fracture and perfect cleavage on {110} and weaker on {001}. The calculated density based on the empirical formula is 4.02 g/cm 3 . Mathesiusite is colorless in fragments, uniaxial (-), with ω = 1.634(3) and ε = 1.597(3). Electron microprobe analyses (average of 7) provided: K 2 O 12.42, SO 3 18.04, V 2 O 5 4.30, UO 3 61.46, H 2 O 3.90 (structure), total 100.12 (all in wt%). The empirical formula (based on 33 O atoms pfu) is: K 4.87 (U 0.99 O 2 ) 4 (S 1.04 O 4 ) 4 (V 0.87 O 5 )(H 2 O) 4 . The eight strongest powder X-ray diffraction lines are [ d obs in Å ( hkl ) I rel ]: 10.64 (110) 76, 7.486 (200) 9, 6.856 (001) 100, 6.237 (101) 85, 4.742 (310) 37, 3.749 (400) 27, 3.296 (401) 9, and 2.9409 (510) 17. The crystal structure of mathesiusite was solved from single-crystal X-ray diffraction data and refined to R 1 = 0.0520 for 795 reflections with I > 3σ( I ). It contains topologically unique heteropolyhedral sheets based on [(UO 2 ) 4 (SO 4 ) 4 (VO 5 )] 5- clusters. These clusters arise from linkages between corner-sharing quartets of uranyl pentagonal bipyramids, which define a square-shaped void at the center that is occupied by V 5+ cations. Each pair of uranyl pentagonal bipyramids shares two vertices of SO 4 tetrahedra. Each SO 4 shares a third vertex with another cluster to form the sheets. The K + cations are located between the sheets, together with a single H 2 O group. The corrugated sheets are stacked perpendicular to c . These heteropolyhedral sheets are similar to those in the structures of synthetic uranyl chromates. Raman spectral data are presented confirming the presence of UO 2 2+ , SO 4 , and molecular H 2 O.

The accumulation of metals and metalloids in diagenetic pyrite framboids is of interest because framboids can be a sink for heavy metal contaminants, a source of metals in ore deposits, and a tool to interpret paleo-ocean chemistry. In this study, we have used laser ablation-inductively coupled plasmamass spectrometry (LA-ICPMS) to analyze pyrite framboids from both the contaminated Derwent Estuary and the uncontaminated Huon Estuary in Tasmania, Australia. While the enrichment of many trace metals in the Huon Estuary followed expected trends, the trends in the Derwent were quite different. In addition to the expected high contents of Pb, Zn, and Cu in the contaminated interval it was found that several elements are not as strongly incorporated into pyrite within the contaminated zone. It is suggested that this is due to over-competition for adsorption sites on the growing iron sulfides in the contaminated zone resulting in diffusion of several elements to deeper levels in the sediments. This results in an increase of these elements in pyrite below the zone of major contamination. The LAICPMS technique also provided the opportunity to obtain accurate data on gold, silver, and tellurium in pyrite, something rarely achieved in sequential leach extractions due to the low concentrations of these metals observed in nature.

Carbonate-substituted hydroxylapatite is the inorganic component in bone. The nanometer size of bone crystallites and their interweaving with subequal volumes of collagen fibrils make the chemical analysis of the bone mineral extremely difficult. The few chemical analyses that are available commonly were made on ashed bone, which, in addition to mineral, also includes chemical residues of collagen. For the present study, we chose the rostrum of the whale Mesoplodon densirostris . Its mineral content of up to 96 wt% makes it an ideal material for pursuing the chemistry of bioapatite within bone. Both bulk (X-ray fluorescence, thermogravimetry, and carbon analysis) and point analyses and element mapping (electron microprobe) were applied to this densest of bone materials. Its bioapatite has an average carbonate content of ~ 8 wt% and an average Ca/P atomic ratio of 1.7. The rostrum shows extremely low-concentration trace elements (Al, Si, Fe, Ti, and Sr) and some minor elements (K and Cl) as in typical bone materials. Homogeneity of elemental distribution is demonstrated in typical mineral-dominated areas within the rostrum sections except around a few vascular holes and vessels. The very good correlation between electron microprobe point analyses and the XRF bulk analyses of the rostrum indicate the latter to be a useful chemical model of bone mineral. The bulk analysis shows that the bioapatite in the rostrum has an average composition of (Ca 8.40 Mg 0.20 Na 0.54 ) [(PO 4 ) 4.87 (CO 3 ) 1.13 ](OH) 0.87 .

During a nanomineralogy investigation of the Allende meteorite with analytical scanning electron microscopy, two new minerals were discovered; both occur as micro- to nano-crystals in an ultrarefractory inclusion, ACM-1. They are allendeite, Sc 4 Zr 3 O 12 , a new Sc- and Zr-rich oxide; and hexamolybdenum (Mo,Ru,Fe,Ir,Os), a Mo-dominant alloy. Allendeite is trigonal, R 3̄, a = 9.396, c = 8.720, V = 666.7 Å 3 , and Z = 3, with a calculated density of 4.84 g/cm 3 via the previously described structure and our observed chemistry. Hexamolybdenum is hexagonal, P 6 3 / mmc , a = 2.7506, c = 4.4318 Å, V = 29.04 Å 3 , and Z = 2, with a calculated density of 11.90 g/cm 3 via the known structure and our observed chemistry. Allendeite is named after the Allende meteorite. The name hexamolybdenum refers to the symmetry (primitive hexagonal) and composition (Mo-rich). The two minerals reflect conditions during early stages of the formation of the Solar System. Allendeite may have been an important ultrarefractory carrier phase linking Zr-,Sc-oxides to the more common Sc-,Zr-enriched pyroxenes in Ca-Al-rich inclusions. Hexamolybdenum is part of a continuum of high-temperature alloys in meteorites supplying a link between Os- and/or Ru-rich and Fe-rich meteoritic alloys. It may be a derivative of the former and a precursor of the latter.

Hutcheonite (IMA 2013-029), Ca 3 Ti 2 (SiAl 2 )O 12 , is a new garnet mineral that occurs with monticellite, grossular, and wadalite in secondary alteration areas along some cracks between primary melilite, spinel, and Ti,Al-diopside in a Type B1 Fractionation and Unidentified Nuclear effects (FUN) Ca-Alrich inclusion (CAI) Egg-3 from the Allende CV (Vigarano type) carbonaceous chondrite. The mean chemical composition of type hutcheonite by electron probe microanalysis is (wt%) CaO 34.6, TiO 2 25.3, SiO 2 20.9, Al 2 O 3 15.7, MgO 2.1, FeO 0.7, V 2 O 3 0.5, total 99.8, giving rise to an empirical formula of Ca 2.99 (Ti 4+ 1.53 Mg 0.25 Al 0.17 Fe 2+ 0.05 V 3+ 0.03 )(Si 1.68 Al 1.32 )O 12 . The end-member formula is Ca 3 Ti 2 (SiAl 2 )O 12 . Hutcheonite has the Ia 3̄ d garnet structure with a = 11.843 Å, V = 1661.06 Å 3 , and Z = 8, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.86 g/cm 3 . Hutcheonite is a new secondary phase in Allende, apparently formed by iron-alkali-halogen metasomatic alteration of the primary CAI phases like melilite, perovskite, and Ti,Al-diopside on the CV chondrite parent asteroid. Formation of the secondary Ti-rich minerals like hutcheonite during the metasomatic alteration of the Allende CAIs suggests some mobility of Ti during the alteration. The mineral name is in honor of Ian D. Hutcheon, a cosmochemist at Lawrence Livermore National Laboratory, California, U.S.A.

Moganite, a newly approved mineral, is microcrystalline silica. Samples of microcrystalline silica varieties containing variable amounts of moganite have been analyzed using absorption infrared spectroscopy (IR). The main spectral differences between moganite and α-quartz occur in the wavenumber region below 650 cm -1 . Above this wavenumber, the frequencies of Si-O stretching vibrations of moganite are almost identical to those of quartz. Additional moganite bands were recorded near 165, 207, 296, 343, 419, 576, and 612 cm -1 , and several of these extra IR bands have been identified for the first time in moganite. The results indicate that moganite and quartz have different crystal structures and symmetries in terms of different tetrahedral linkages. Infrared spectra obtained from samples with different moganite contents cannot be simply explained by mechanical mixing of the two moganite and quartz end phases. The change in moganite content leads to not only a variation of spectral intensity, but also a systematic modification in band position and full-width at half maximum. This unusual behavior is attributed to grain size, strains, and stacking faults in moganite and the intergrowth of moganite with fine-grained quartz. The close correlation between band width and moganite content is indicative of an improved crystallinity with decreasing in moganite concentration that has been identified in natural quartz variations. The results imply that moganite may play a role in the formation or crystallization of microcrystalline quartz. The present IR application offers a new method to estimate the moganite content in microcrystalline silica varieties.

The mechanism of kaolinite transformation into dickite has been investigating using 13 samples from the Frøy and Rind oil fields (Broad Fourteens basin, North Sea), 3 kaolinite specimens with different crystal order (KGa-2, Kaolinite API 17, Keokuk kaolinite), and 2 dickite-rich samples (Natural History Museum collection). Detailed analysis of XRD, thermal analysis, and SEM data show that: (1) as dickite content increases, there is also an increase of the crystal order of kaolinite; (2) in dickite-rich specimens kaolinite and dickite have crystals (or XRD-coherent domains) of the same size; (3) there is no specific dehydroxylation temperature for each polytype, rather particle size and crystal order control dehydroxylation temperature independently of polytype; (4) with progressive dickite content, the development of both particle size and the size of the coherent crystal domains within particles is greater in the c direction than in the a - b plane; (5) the growth of defect-free segments in the c direction is not connected with the growth in the a and b directions, as would be expected in crystallization from solution; (6) textural features indicate coalescence of kaolin plates with burial; (7) there is a very weak positive correlation between particle dimensions and relative kaolinite-dickite content. These results are interpreted as resulting from a double reaction taking place in the solid state with burial. Some kaolinite domains grow in size and crystal order while other domains are transformed into dickite. Presumably, also the dickite domains formed early in the transformation grow in crystal order. The transformation into dickite stops at 90-95% dickite because the remaining kaolinite domains are so large and stable that the stability increase produced by the polytype transformation would be negligible.

Knowledge and understanding about radionuclides retention processes on the materials composing the engineered barrier (clay mineral and metallic container waste) are required to ensure the safety and the long-term performance of radioactive waste disposal. Therefore, the present study focuses on the competitiveness of clay and the metallic container in the process of adsorption/desorption of the radionuclides simulators of Am 3+ and UO 2 2+ . For this purpose, a comparative study of the interaction of samarium (chosen as chemical analog for trivalent americium) and zirconyl (as simulator of uranyl and tetravalent actinides) with both FEBEX bentonite and metallic container, under subcritical conditions, was carried out. The results revealed that the AISI-316L steel container, chemical composition detailed in Table 1, immobilized the high-radioactive waste (HRW), even during the corrosion process. The ZrO 2+ was irreversibly adsorbed on the minireactor surface. In the case of samarium SEM/EDX analysis revealed the formation of an insoluble phase of samarium silicate on the container surface. There was no evidence of samarium diffusion through the metallic container. Samarium remained adsorbed by the container also after desorption experiment with water. Therefore, steel canister is actively involved in the HRW immobilization.

The effect of the substitution of Ca with Co, on the phase transition and on the extension of the miscibility gap, was studied to model the general mechanism of phase transitions and solid solutions in (Ca,M 2+ )M 2+ Si 2 O 6 pyroxenes. Eleven pyroxenes with composition Ca 1-x Co 1+x Si 2 O 6 , (0 ≤ x ≤ 1) were therefore synthesized by piston cylinder at P = 3 GPa, and T between 1100 and 1350 °C. The samples were characterized by SEM-EDS, XRD powder diffraction, and TEM. The results were compared with those of Ca-Fe and Ca-Mg pyroxenes. The phase diagram of Ca-Co pyroxenes is similar to that of Ca-Fe and Ca-Mg ones, with a wide asymmetric miscibility gap, and higher solubility in the Ca-rich side of the gap. The solubility on the Ca-rich side of the gap is related to the radius of the cation substituting. The cell parameters of the Ca-Co pyroxenes undergo a sudden change at the composition of about 0.4 Ca apfu, due to the C 2/ c - P 2 1 / c phase transition. The change in volume with composition follows an ideal trend, in the C 2/ c phase, dictated by the ionic size of the substituting cation. Deviation from the C 2/ c behavior are instead observed in the P 2 1 / c field and ascribed to volume strain. The same turnover was found in Ca-Mg, Ca-Fe, and Ca-Mn pyroxenes. The C 2/ c - P 2 1 / c transition occurs with decreasing the M2 average cation radius, down to a critical value between 0.85 and 0.88 Å, depending on the series. A stabilization of the C 2/ c phase related to crystal field in Ca-Fe and Ca-Co pyroxenes is suggested by the analysis of the volume strain in the P 2 1 / c field. A key finding is that a miscibility gap may develop either by lattice strain related to cation substitution, within a series where all endmembers have the same structure, or for the combined effect of lattice strain and a phase transition, as is the case for pyroxenes.

Infrared spectroscopy and X-ray diffraction are used to evaluate the OH and H 2 O environments in 10 Å phase (“TAP”), nominally Mg 3 Si 4 O 10 (OH) 2 ·H 2 O. Two partially deuterated samples of TAP synthesized under different conditions have very similar IR spectra, indicating that the phase has a reproducible structural state. IR spectra were also collected of samples of fully Ni-substituted and partially deuterated TAP, and of samples heated for 1-2 h at 500 °C to remove structural H 2 O/D 2 O and leave behind bands due to OH/OD of the 2:1 layer. A high-pressure study of the Ni-TAP sample confirmed that the behavior of its H 2 O and OH/OD bands was analogous to that observed in previous studies of Mg-TAP. Comparison of the IR spectra of unheated, heated, and compressed samples has allowed three different types of Mg-OH (Mg-OD) stretching bands to be identified, two of which are further split, indicating subtle complexities in the TAP structure. The third band is identical to the band in talc. Two interlayer H 2 O stretching bands have been identified. The presence of an absorption feature that is broader than these interlayer H 2 O bands suggests that there is a second type of more weakly bonded H 2 O. On heating to 500 °C, the main interlayer H 2 O bands are lost, the talc-like band is unchanged, and shifts in the other Mg-OH band frequencies indicate a change in environment following the loss of the interlayer H 2 O. At the same time the signature of a silanol group is possibly revealed from the coincidence of band positions in the Mg-TAP and Ni-TAP spectra. The recognition of three distinct Mg-OH (Ni-OH) environments in Mg-TAP (Ni-TAP) is consistent with the structural model of TAP proposed by Welch et al. (2006) and Phillips et al. (2007), in which the transformation from talc to TAP involves a key change from hydrophobic to hydrophilic character that enables hydration of the interlayer. A final level of complexity is indicated by the identification of a 3 c trigonal superstructure from single-crystal XRD, implying a structure analogous to that of the 3 T phengite polytype, with interlayer H 2 O fulfilling the role of K. The formation of additional OH groups when talc transforms to 10 Å phase increases the amount of water contained in 10 Å phase and may also occur in closely related phyllosilicates in the Earth’s mantle, such as intergrowths of chlorite with 10 Å phase. Moreover, the reproducibility of the key features of the IR spectra for different samples implies that this water content is fixed.

FeSi remains crystalline up to at least 2350 (±200) K at 23 GPa and 2770 (±200) K at 47 GPa in a laser-heated diamond-anvil cell, showing that addition of silicon does not cause a large amount of melting point depression; the melting temperature of pure iron ranges from 2300 (±100) K to 2700 (±150) K between 20 and 50 GPa. The transition between e (B20) and B2 (CsCl-structured) crystalline phases occurs at 30 (±2) GPa at all temperatures from 1200 to 2400 K. The resulting 5% density increase may cause an increase in the miscibility of silicon in iron at P > 30 GPa, with potential implications for the cores of small rocky planets such as Mars and Mercury.

The infrared spectra of hydroxyl in synthetic hydrous wadsleyite (β-Mg 2 SiO 4 ) and ringwoodite (γ-Mg 2 SiO 4 ) were measured at room temperature up to ∼18.8 GPa for wadsleyite and up to ∼21.5 GPa for ringwoodite. High-temperature spectra were measured in an externally heated diamond-anvil cell up to 650 °C at ∼14.2 GPa for wadsleyite and up to 900 °C at ∼18.4 GPa for ringwoodite. The synthetic samples reproduce nearly all the important OH bands previously observed at ambient conditions. Only subtle changes were observed in the infrared spectra of both minerals, both upon compression at room temperature and upon heating at high pressure. For wadsleyite, upon compression to ∼18.8 GPa, the frequencies of the bands at ∼3600 cm -1 remain almost unchanged, while the main bands at 3200-3400 cm -1 shift to lower frequencies. During heating at 14.2 GPa to 650 °C the bands at 3200-3400 cm -1 broaden and shift to slightly lower frequencies. For ringwoodite, upon compression to ∼21.5 GPa, the main bands at 3115 cm -1 progressively shift to lower frequencies. During heating at 18.4 GPa to 900 °C, no frequency shift was observed for the band at ∼3700 cm -1 , but the band initially at ∼3115 cm -1 shifts very slightly to higher frequencies, which should yield almost the same band positions at 1300-1400 °C as those measured at ambient conditions. Our data suggest that water speciation in hydrous wadsleyite and ringwoodite at ambient conditions may be comparable to that under mantle conditions, except perhaps for subtle changes in hydrogen bonding. The low OH-stretching frequencies in wadsleyite and ringwoodite under transition zone conditions imply a large H/D fractionation during degassing of the deep mantle. This may explain the apparent disequilibrium between the hydrogen isotopic composition of the upper mantle and the ocean.

Knowledge of the thermodynamic mixing properties of amphiboles whose compositions lie along the tremolite-glaucophane join is of interest to those studying high-pressure metamorphic rocks as well as rocks transitional between the greenschist and blueschist facies. This study is the second of a two-part investigation of the tremolite-glaucophane join, with the first study (Jenkins et al. 2013) devoted to the volume composition and crystal chemical relations, and the current study focused on defining the location and extent of asymmetry of the miscibility gap (solvus) along this join. A series of experiments was done over the temperature range of 500-800 °C at pressures of 1.6-1.9 GPa to determine the location of the miscibility gap using both two-amphibole dissolution experiments, including time-series experiments at 700, 750, and 800 °C lasting up to 670 h, as well as various endmember and intermediate amphibole overgrowth techniques to approach the boundary from different compositional directions. These results, which placed some important limits on the location of the miscibility gap, were combined with an autocorrelation analysis of the mid- and far-infrared spectra of single-phase amphiboles formed in the first study (Jenkins et al. 2013) to refine the shape of the miscibility gap. Derived values of the relative change in the autocorrelation parameter (dD Corr ) were fairly constant over all of the frequency ranges analyzed and indicated that the miscibility gap is steeper at the glaucophane-rich compared to tremolite-rich side of the binary join. Combining the compositional re-equilibration experiments with the infrared autocorrelation results permitted deriving the ratio of the parameters α Gl /α Tr = 0.5 and W TrGl = 67-70 kJ using asymmetric formalism theory. The calculated boundary has a critical-point temperature that falls in the range of 760-800 °C in this iron-free system. The asymmetry of the calculated miscibility gap appears to be confirmed by amphibole pairs in nature. The implications of this study are that this technique of combining compositional re-equilibration experiments with autocorrelation analysis of single-phase solid solutions is a potentially powerful method of locating miscibility gaps at low temperatures and for chemically complex binary joins. It is also suggested that the miscibility gaps presented here provide a basis for interpreting the degree of equilibrium reached in assemblages with complexly zoned or intergrown amphiboles.

Thermophysical and thermochemical calorimetric investigations were carried out on synthetic analogs of two minerals: cobaltomenite (CoSeO 3 ·2H 2 O) and ahlfeldite (NiSeO 3 ·2H 2 O). The synthesis was realized by mixing of aqueous solutions of cobalt and nickel nitrates, accordingly, and sodium selenite, acidified with the help of a solution of nitric acid and characterized by X-ray powder diffraction and FTIR spectroscopy methods. The low-temperature heat capacities of CoSeO 3 ·2H2O and NiSeO 3 ·2H 2 O were measured using adiabatic calorimetry between 8 and 340 K, and the third-law entropies were determined. Values of S ° (298 K, CoSeO 3 ·2H 2 O, cr.) = 183.2 ± 1.0 J/(mol·K) and S ° (298 K, NiSeO 3 ·2H 2 O, cr.) = 172.9 ± 1.0 J/(mol·K) are obtained with an uncertainty of 0.5%. The enthalpies of formation for CoSeO 3 ·2H 2 O and NiSeO 3 ·2H 2 O were determined by solution calorimetry with H 2 SO 4 solution as the solvent and giving Δf H ° (298 K, CoSeO 3 ·2H 2 O, cr.) = -1135.3 kJ/mol, Δf H ° (298 K, NiSeO 3 ·2H 2 O, cr.) = -1133.3 kJ/mol. The Gibbs energy of formation for CoSeO 3 ·2H 2 O and NiSeO 3 ·2H 2 O at T = 298 K, 1 atm can be calculated on the basis on Δf H ° and Δf S °:Δf G ° (298 K, CoSeO 3 ·2H 2 O, cr.) = -937.4 kJ/mol and Δf G ° (298 K, NiSeO 3 ·2H 2 O, cr.) = -932.4 kJ/mol. Smoothed CP °( T ) values between T = 0 K and T = 320 K for CoSeO 3 ·2H 2 O (cr.) and NiSeO 3 ·2H 2 O (cr.) are presented along with values for S° and the functions [ H °( T )- H °(0)] and [ G °( T )- H °(0)]. These results motivate a re-evaluation of the natural conditions under which selenites, and selenates replace selenides, and sulfides in the oxidation zones of sulfide ore deposits or upon weathering of technologic waste. The values of Δ fG ° for CoSeO 3 ·2H 2 O and NiSeO 3 ·2H 2 O were used to calculate the Eh-pH diagrams of the Co-Se-H 2 O and Ni-Se-H 2 O systems. These diagrams have been constructed for the average contents of these elements in acidic waters of the oxidation zones of sulfide deposits. The behavior of selenium, cobalt, and nickel in surface environments have been quantitatively explained by variations of the redox potential and the acidity-basicity of the mineral-forming medium. Precisely these parameters determine the migration ability of selenium compounds and its precipitation in the form of various solid phases.

Despite the number of detailed studies on arsenate adsorption onto synthetic 2-line ferrihydrite carried out during the past few decades, questions remain regarding the fate of adsorbed arsenate during phase transformation of this poorly crystalline iron oxy-hydroxide. We assessed arsenate partitioning during this transformation by aging synthetic 2-line ferrihydrite with adsorbed arsenate (at an As/Fe molar ratio of ~ 0.017) for 7 days at 75 °C under highly alkaline conditions (pH ~ 10). X-ray diffraction patterns show that ~ 55% of the ferrihydrite converted almost entirely to hematite (with traces of goethite) after aging 7 days, accompanied by a ~ 54% loss of reactive surface area (BET). ICP-MS analyses indicate that despite this conversion and significant loss of surface area, the aqueous arsenate concentration decreased from ~ 1.48 to ~ 0.51 mg/L during the course of the experiment. XAS analyses suggest that the concentration of arsenate and its speciation are controlled by its incorporation into the hematite.

High-pressure behavior of coesite was studied on single crystals using diamond-anvil cells with neon as the pressure-transmitting medium by means of in situ Raman spectroscopy up to pressures of ~ 51 GPa. The experimental observations were complemented with theoretical computations of the Raman spectra under similar pressure conditions. We find that coesite undergoes two phase transitions and does not become amorphous at least up to ~ 51 GPa. The first phase transition (coesite I to coesite II) is reversible and occurs around 23 GPa. The second transition (coesite II to coesite III) at about 35 GPa is also reversible but involves a large hysteresis. Samples recovered from the highest pressure achieved, ~ 51 GPa, show Raman spectra of the initial coesite. The ab initio calculations gave insight into the initiation mechanism of the first phase transition, implying, from the analysis of unstable phonon modes, that it is probably a displacive phase transition due to shearing of the four-membered rings of SiO4 tetrahedra upon compression. The transition to the lowest-symmetry phase, coesite III, is possibly a first-order phase transition that leads to a very distinct structure. None of the metastable high-pressure phases of coesite has been previously studied and it was widely accepted that coesite undergoes pressure-induced amorphization at significantly lower pressures (30 GPa). The study of the high-pressure behavior of coesite is important to better constrain the metastable phase diagram of silica. Further crystallographic investigations are necessary for characterizing the structures of these metastable coesite forms. Crystalline or amorphous metastable phases derived from coesite under high-pressure conditions are of particular interest because they can be used as potential tracers of peak transient pressures (stress) reached in processes such as impacts or faulting.

Qingsongite (IMA 2013-30) is the natural analog of cubic boron nitride (c-BN), which is widely used as an abrasive under the name “Borazon.” The mineral is named for Qingsong Fang (1939-2010), who found the first diamond in the Luobusa chromitite. Qingsongite occurs in a rock fragment less than 1 mm across extracted from chromitite in deposit 31, Luobusa ophiolite, Yarlung Zangbu suture, southern Tibet at 29°13.86N and 92°11.41E. Five electron microprobe analyses gave B 48.54 ± 0.65 wt% (range 47.90-49.2 wt%); N 51.46 ± 0.65 wt% (range 52.10-50.8 wt%), corresponding to B1.113N0.887 and B1.087N0.913, for maximum and minimum B contents, respectively (based on 2 atoms per formula unit); no other elements that could substitute for B or N were detected. Crystallographic data on qingsongite obtained using fast Fourier transforms gave cubic symmetry, a = 3.61 ± 0.045 Å. The density calculated for the mean composition B 1.100 N 0.900 is 3.46 g/cm 3 , i.e., qingsongite is nearly identical to synthetic c-BN. The synthetic analog has the sphalerite structure, space group F 43 m. Mohs hardness of the synthetic analog is between 9 and 10; its cleavage is {011}. Qingsongite forms isolated anhedral single crystals up to 1 mm in size in the marginal zone of the fragment; this zone consists of ~ 45 modal% coesite, ~ 15% kyanite, and ~ 40% amorphous material. Qingsongite is enclosed in kyanite, coesite, or in osbornite; other associated phases include native Fe; TiO 2 II, a high-pressure polymorph of rutile with the αPbO 2 structure; boron carbide of unknown stoichiometry; and amorphous carbon. Coesite forms prisms several tens of micrometers long, but is polycrystalline, and thus interpreted to be pseudomorphic after stishovite. Associated minerals constrain the estimated pressure to 10-15 GPa assuming temperature was about 1300 °C. Our proposed scenario for formation of qingsongite begins with a pelitic rock fragment that was subducted to mid-mantle depths where crustal B originally present in mica or clay combined with mantle N (δ 15 N = -10.4 ± 3‰ in osbornite) and subsequently exhumed by entrainment in chromitite. The presence of qingsongite has implications for understanding the recycling of crustal material back to the Earth’s mantle since boron, an essential constituent of qingsongite, is potentially an ideal tracer of material from Earth’s surface.

The subsolidus and melting phase relations in the CaCO 3 -siderite system have been studied in multianvil experiments using graphite capsules at pressure of 6 GPa and temperatures of 900-1700 °C. At low temperatures, the presence of ankerite splits the system into two partial binaries: siderite + ankerite at 900 °C and ankerite + aragonite up to 1000 °C. Extrapolated solvus curves intersect near 50 mol% just below 900 °C. At 1100 and 1200 °C, the components appear to form single-phase solid solutions with space group symmetry R 3 c , while CaCO 3 maintains aragonite structure up to 1600 °C and 6 GPa. The FeCO 3 solubility in aragonite does not exceed 1.0 and 3.5 mol% at 900-1000 and 1600 °C, respectively. An increase of FeCO 3 content above the solubility limit at T > 1000 °C, leads to composition-induced phase transition in CaCO 3 from aragonite, Pmcn , to calcite, R 3 c , structure, i.e., the presence of FeCO 3 widens the calcite stability field down to the P-T conditions of sub-cratonic mantle. The siderite-CaCO3 diagram resembles a minimum type of solid solutions. The melting loop for the FeCO 3 -CaCO 3 join extends from 1580 °C (FeCO 3 ) to 1670 °C (CaCO 3 ) through a liquidus minimum near 1280 ± 20 °C and 56 ± 3 mol% CaCO 3 . At X (Ca) = 0-30 mol%, 6 GPa and 1500-1700 °C, siderite melts and dissolves incongruently according to the reaction: siderite = liquid + fluid. The apparent temperature and X (Ca) range of siderite incongruent dissolution would be determined by the solubility of molecular CO 2 in (Fe,Ca)CO 3 melt. The compositions of carbonate crystals and melts from the experiments in the low-alkali carbonated eclogite (Hammouda 2003; Yaxley and Brey 2004) and peridotite (Dasgupta and Hirschmann 2007; Brey et al. 2008) systems are broadly consistent with the topology of the melting loop in the CaCO 3 - MgCO 3 -FeCO 3 system at 6 GPa pressure: a Ca-rich dolomite-ankerite melt coexists with Mg-Fe-calcite in eclogites at CaO/MgO > 1 and Mg-dolomite melt coexists with magnesite in peridotites at CaO/MgO < 1. However, in fact, the compositions of near solidus peridotite-derived melts and carbonates are more magnesian than predicted from the (Ca,Mg,Fe)CO3 phase relations.

This work was carried out within the framework of the European Space Agency and Japanese Aerospace Exploration Agency BepiColombo space mission to Mercury and intends to provide valid tools for the interpretation of spectra acquired by the MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS) on board of BepiColombo. Two C 2/ c augitic pyroxenes, with different Mg/Fe ratios and constant Ca contents, were investigated by in situ high-temperature thermal infrared spectroscopy and in situ high-temperature single-crystal X-ray diffraction up to temperatures of about 750 and 770 K, respectively. The emissivity spectra of the two samples show similar band center shifts of the main three bands toward lower wavenumbers with increasing temperature. In detail, with increasing temperature bands 1 and 2 of both samples show a much stronger shift with respect to band 3, which remains almost unchanged. Our results indicate that the center positions of bands 1 and 2 are strong functions of the temperature, whereas the center position of band 3 is a strong function of the Mg# [with Mg# = Mg/ (Mg + Fe 2+ ) atomic ratio]. The analysis of the thermal behavior gives similar thermal expansion volume coefficients, α V, for the Mg-rich and Fe-rich samples, with α V = 2.72(8) and 2.72(7) × 10 -5 K -1 , respectively, using the Berman (1988) equation. This correspondence totally explains the band center shifts similarity between the two samples. Our data suggest that MERTIS spectra will be able to provide indications of C 2/ c augitic pyroxene Mg# and will allow a correct interpretation that is independent on the spectra acquisition temperature.

The Lengenbach (Switzerland) Pb-As-Tl-Zn deposit was formed from a sulfide melt at about 500 °C during Alpine metamorphism, but details on its formation and especially the source of the metals are still under debate. In this study we present two sample sets to address these questions: (1) MC-ICP-MS analyses of thallium isotopes in sulfides, sulfosalts, and melt inclusions from the Alpine metamorphic Lengenbach deposit in the Binn Valley of Switzerland, the non-metamorphic Wiesloch Mississippi Valley-type deposit in Southern Germany, and the Cu- and As-rich mineralization at Pizzo Cervandone about 2 km SW of the Lengenbach deposit, which has been discussed as potential source of the Lengenbach metals. (2) LA-ICP-MS analyses of micas from the Lengenbach deposit and surrounding country rocks between the deposit and the Pizzo Cervandone to trace potential metal-bearing fluid pathways. We found that Tl isotope compositions expressed as ε 205 Tl values in all investigated samples range from -4.1 ± 0.5 to +1.9 ± 0.5. The whole variation can be seen in the Lengenbach deposit alone, which hence records considerable fractionation even during high-temperature processes involving a sulfide melt. This large range of ε 205 Tl is thought to be caused by nuclear volume-dependent fractionation. Interestingly, the common fahlores at Lengenbach behave differently from all other investigated sulfosalts: based on their heavy isotopic composition together with a low As/S-ratio, they do not seem to be crystallized from the sulfide melt, but are interpreted to have formed from hydrothermal fluids enriched in the heavy Tl isotopes. Although As mobilization in the gneisses and dolomites surrounding the Lengenbach deposit is evident based on secondary arsenites, no traces of such a country rock fluid could be found in fissure micas at Lengenbach. Hence, considerations involving K/Rb, Rb/Tl, As/S, and Pb/Tl ratios in the sulfides and micas imply that the element enrichment in the Lengenbach deposit is either pre-Alpine or related to peak metamorphism, but occurred definitely before mica growth at Lengenbach.

Fluorowardite (IMA2012-016), NaAl 3 (PO 4 )2(OH) 2 F 2 ·2H 2 O, the F analog of wardite, is a new mineral from the Silver Coin mine, Valmy, Iron Point district, Humboldt County, Nevada, U.S.A., where it occurs as a low-temperature secondary mineral in complex phosphate assemblages rich in Al, Na, and F. Fluorowardite forms colorless to white or cream-colored, tetragonal-pyramidal crystals up to 0.1 mm in diameter. The streak is white. Crystals are transparent to translucent, with vitreous to pearly luster. The Mohs hardness is about 5, the tenacity is brittle, the fracture is irregular, and crystals exhibit one perfect cleavage on {001}. The calculated density is 2.760 g/cm 3 . Optically, fluorowardite is uniaxial positive, with ω = 1.576(2) and ε = 1.584(2) (white light) and is non-pleochroic. Electron microprobe analyses (average of 8) provided: Na 2 O 6.27, CaO 1.74, MgO 0.42, Al 2 O 3 35.21, Fe 2 O 3 0.72, P 2 O 5 32.49, As 2 O 5 0.64, F 6.76, O=F -2.85, H 2 O 13.35 (structure), total 94.74 wt%. The presence of H 2 O and OH and the absence of CO 3 were confirmed by FTIR spectroscopy. The empirical formula (based on 14 anions) is: (Na 0.87 Ca 0.13 Mg 0.04 ) Σ1.04 (Al 2.96 Fe 3+ 0.04 ) Σ3.00 (P 1.96 As 0.03 )Σ 1.99 O 8.12 (OH) 2.35 F 1.53 ·2H 2 O. Fluorowardite is tetragonal, P 4 1 2 1 2, a = 7.077(2), c = 19.227(3) Å, V = 962.8(5) Å 3 , and Z = 4. The eight strongest lines in the X-ray powder diffraction pattern are [ d obs in Å( I )( hkl )]: 4.766(100)(004,103); 3.099(75) (211,203); 3.008(62)(115,212); 2.834(28)(204,213); 2.597(56)(205); 1.7628(32)(400,401); 1.6592(29) (multiple); and 1.5228(49)(423, 2·2·10). The structure of fluorowardite ( R 1 = 3.15% for 435 F o > 4σ F ) contains layers parallel to {001} consisting of Alφ 6 (φ = F, O, OH or H 2 O) octahedra, PO 4 tetrahedra, and NaO 6 (H 2 O)2 polyhedra. The two independent Alφ 6 octahedra link by corner-sharing to form a square array. Each PO 4 tetrahedron shares corners with three adjacent octahedra in the same square array and a fourth corner with an octahedron in the next layer. The Na atoms reside in the “cavities” in the square array, forming bonds only to O atoms in the same layer. Of the two nearly identical OH sites in the wardite structure, only one is occupied by F in the fluorowardite structure. This is an interesting example of a structure in which OH and F are selectively incorporated into two different, but similar, sites as the result of rather subtle hydrogen bonding influences.

Correianevesite, ideally Fe 2+ Mn 2 2+ (PO 4 ) 2 ·3H 2 O, is a new reddingite-group mineral approved by the CNMNC (IMA 2013-007). It occurs in a phosphate-rich granite pegmatite that outcrops near the Cigana mine, Conselheiro Pena, Rio Doce valley, Minas Gerais, Brazil. Associated minerals are: triphylite, lithiophilite, frondelite, rockbridgeite, eosphorite, vivianite, fairfieldite, leucophosphite, cyrilovite, phosphosiderite, etc. Correianevesite occurs as grayish-brown to reddish-brown transparent bipyramidal crystals up to 4 mm in size. The streak is white, and the luster is vitreous. Mohs hardness is 3½. Cleavage is poor on (010). Fracture is laminated, uneven across cleavage. The measured density is 3.25(2) g/cm 3 ; the calculated density is 3.275 g/cm3. The mineral is biaxial (+), α = 1.661(5), β = 1.673(5), γ = 1.703(5), 2V meas = 70(10)°, 2V calc = 65.6°. The IR spectrum confirms the presence of H 2 O. The Mössbauer spectrum shows the presence of two sites for Fe 2+ and one site for Fe 3+ occupied in the ratio Fe1 2+ :Fe2 2+ :Fe 3+ = 39:55:6. The chemical composition is as follows (electron microprobe, H 2 O determined by gas chromatography of ignition products, Fe apportioned between FeO and Fe 2 O 3 based on Mössbauer data, wt%): MnO 29.21, FeO 21.74, Fe 2 O 3 1.54, P 2 O 5 34.59, H 2 O 12.6, total 99.68. The empirical formula, based on 11 O apfu, is H 5.78 Mn 1.70 Fe 2+ 1.25 Fe 3+ 0.08 P 2.015 O 11 . The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 5.08 (43) (020), 4.314 (28) (002, 210), 3.220 (100) (221, 202), 3.125 (25) (122), 2.756 (35) (103, 230), 2.686 (25) (222, 113), 2.436 (22) (123), and 2.233 (23) (411, 331). The crystal structure is solved (R 1 = 0.0176). Correianevesite is orthorhombic, space group Pbna, a = 9.4887(2), b = 10.1149(2), c = 8.7062(2) Å, V = 835.60(3) Å 3 , Z = 4. The refined crystal-chemical formula is: (Fe 2+ 0.72 Mn 2+ 0.20 Fe 3+ 0.08 )(Mn 1.48 Fe 2+ 0.52 )(PO 4 ) 2 (H 2 O,OH) 3 .

The crystal structure of Pb 21 [Si 7 O 22 ] 2 [Si 4 O 13 ] has been solved on crystals grown by crystallization from melt. The compound is hexagonal, P 6 3 / m , a = 9.9244(5), c = 34.2357(16) Å, V = 795.28(6) Å 3 , R 1 = 0.042 for 3361 unique observed reflections. The structure contains five symmetrically independent Si sites tetrahedrally coordinated by O atoms. The Si1O 4 , Si3O 4 , and Si4O 4 tetrahedra share corners to form branched heptameric [Si 7 O 22 ] 16- units, whereas the Si2O 4 and Si5O 4 tetrahedra form the tetrameric [Si4O13]10- anions. The structure contains six symmetrically independent Pb sites with the PbO n coordination polyhedra distorted due to the stereochemical activity of the lone electron pairs. The structure can be described as a stacking of layers of the two types, A and B. The A-type layer contains [Si 7 O 22 ] 16- units, Pb1, Pb2, Pb3, and Pb4 sites, whereas the B-type layer contains [Si 4 O 13 ] 10- anions, together with Pb5, Pb6, and Pb6A sites. Stacking of the layers can be described as a sequence ...AA′BAA′B..., where A and A′ denote A layers with opposite orientations of the tripod-shaped silicate heptamers. The crystal structure of Pb 21 [Si 7 O 22 ] 2 [Si 4 O 13 ] has many similarities to that of hyttsjöite, which contains the same layers consisting of tripod-shaped [Si 7 O 22 ] 16- anions. In both title compound and hyttsjöite, the anions are stacked together in such a way that ellipsoidal cavities with dimensions of ca. 10 × 6 × 6 Å 3 are created. The cavities are occupied by the ClPb 6 octahedra in hyttsjöite and by “empty” Pb 6 octahedra in Pb 21 [Si 7 O 22 ] 2 [Si 4 O 13 ]. Analysis of structural and chemical complexity in the PbO-SiO 2 system indicates that the most chemically complex phases (in terms of complexity of relations between chemical components) appear to be the most complex from the structural point of view as well. The title phase is the most structurally and chemically complex phase in the system. Structural organization of crystalline phases in the PbO-SiO 2 system can be described as controlled by the Pb:Si ratio. For the phases with Pb:Si <2, their structures contain Pb 2+ ions and silicate anions. For the phases with Pb:Si <2, the structures contain “additional” O atoms, i.e., atoms that are not bonded to Si. These atoms form OPb 4 tetrahedra, which are the next strongest structural subunits in the structure after silicate anions. The structures of the phases with Pb:Si <2 can therefore be described as based upon silicate anions and polynuclear cationic units consisting of edge- and corner-sharing OPb 4 tetrahedra.

The temperature dependence of the unit-cell dimensions and the crystal structures of the fluorperovskite neighborite, NaMgF 3 (analyzed in the Pbnm setting of the space group), have been determined at 88 temperatures between 9 and 440 K from high-resolution, time-of-flight, powder neutron diffraction data. Lattice parameters exhibit saturation at low temperatures, before developing linear thermal expansion coefficients at temperatures above ~ 350 K. The temperature dependence of each axis has been analyzed, and fitted, using a two-term expression related to an Einstein internal energy function. The unit-cell parameters a and c behave in a conventional manner, however, an unexpected, and previously unobserved, region of negative linear thermal expansion has been found for the b axis in the temperature interval 20 ≤ T ≤ 90 K. Estimated, high-temperature axial thermal expansion coefficients derived from the lattice parameter fitting are in good agreement with those experimentally determined from an earlier synchrotron study, and indicate that high-temperature saturation has been achieved in neighborite by 440 K. The unit-cell volume varies smoothly and monotonically over the whole temperature interval, and the two-term Debye model of Barron has been successfully used to fit these data with characteristic temperatures of 369(2) and 1055(14) K. For the temperature interval 313.15-443.15 K, the thermodynamic Grüneisen constant has been determined using the Debye parameterization of the unit-cell volume, coupled with literature values of the isobaric molar heat capacity. The evolution of the crystal structure as a function of temperature is presented, and explained, in terms of the temperature dependence of the amplitudes of the seven symmetry-adapted basis-vectors of the aristotype phase that are consistent with the orthorhombic space group. The calculated temperature variations of the bond lengths are in excellent agreement with those experimentally determined. The primary order parameters for centrosymmetric, zone-boundary phase transitions in perovskite-structured compounds, i.e., the amplitudes of the basis vectors that transform as the irreducible representations R + 4 (anti-phase tilt) and M + 3 (in-phase tilt), have been fitted to a Landau free energy expansion that incorporates low-temperature saturation. Within the temperature range studied, the temperature dependence of the displacement corresponding to the anti-phase tilt is consistent with tricritical behavior. Experimental evidence is presented for a quadratic coupling of the in-phase tilt to the anti-phase tilt for temperatures greater than ~ 135 K, suggesting critical behavior at the orthorhombic-cubic transition is purely related to an instability at the R point of the pseudocubic Brillouin zone.

The crystal chemistry of Cr-spinels included in spinel peridotite mantle xenoliths from Baker Rocks and Greene Point (northern Victoria Land, Antarctica) has been studied by single-crystal structure refinement and electron microprobe analysis. All crystals are characterized by a dominance of Al ↔ Cr substitution with minor evidences of Mg ↔ Fe 2+ substitution and pertain to the Mg-rich portion of the spinel sensu stricto-chromite join. The two groups of samples, Baker Rocks (BR) and Greene Point (GP), show distinct degree of cation order with the inversion parameter ranging from 0.17 to 0.20 for BR spinels and from 0.06 to 0.13 for GP crystals. Closure temperatures, computed by a geothermometer based on the M Al+ T Mg ↔ T Al+ M Mg intracrystalline exchange, range from 883 to 911 °C for BR spinels and from 592 to 675 °C for GP spinels. We show that this difference is due to the higher concentration in Fe 3+ in GP spinels that enabled a faster kinetics of the intracrystalline cation ordering reaction, allowing the GP spinels to reach a higher degree of cation ordering and then lower closure temperatures.

Five spinel single-crystal samples within the ulvöspinel-qandilite series [(Fe 2- x Mg x )TiO 4 , 0.15 < x < 0.94] were synthesized and structurally and chemically characterized by X-ray diffraction and electron microprobe techniques. Site populations, derived from structural and chemical analysis, show that the tetrahedrally coordinated site (T) is exclusively populated by Mg2+ and Fe2+, while the octahedrally coordinated site (M) is populated by Ti 4+ , Mg 2+ , Fe 2+ , and minor amounts of Fe 3+ . The inverse cation distribution is characterized by parallel substitution of Mg 2+ for Fe 2+ at both the T and M sites along the series. The variation in the unit-cell parameter from 8.527 to 8.495 Å is mainly related to the occurrence of Mg 2+ at the M site rather than the T site. In fact, the substitution of Mg 2+ for Fe 2+ yields significant variations in M-O (from 2.045 to 2.034 Å) and only limited variation in T-O (from 2.007 to 2.002 Å). In conjunction with data from the literature, the present study provide a basis for quantitative analyses of the variation in TMg-O bond distance from 1.966 Å for Mg-poor ulvöspinel to 1.990 Å for the qandilite end-member.

Minerals of the amphibole group are found in igneous rocks on Earth and other rocky bodies. Since the O(3) site of amphibole can contain OH, O 2- , F, and Cl, amphibole composition provides important information about water and halogen contents, oxidation state, and other features of its formation and alteration environments. However, the complexity of amphibole crystal chemistry means this information is difficult to extract. Furthermore, it has been regular practice in the era of the electron microprobe to neglect H and Fe 3+ analyses for amphibole, critically reducing the amount of information available in amphibole analyses in the literature. We have assembled models and insights from previous work to create a methodology that allows the estimation of magmatic H 2 O and Cl contents from existing amphibole analyses. Since the methodology requires use of a cation norm, we begin with a deeper investigation of the consequences of different cation normalization schemes for amphibole analyses, and provide grounds for deciding which scheme best fits a given amphibole analysis. We then show how the existing model of Popp and coworkers can be reversed to estimate the OH and [O(3)] O 2- contents of amphiboles in synthesis experiments. Using a synthetic data set collected from the literature (39 amphibole analyses), we calibrate a partitioning model for the OH/Cl competition on the O(3) site of igneous amphiboles K Cl = ( X Cl / X OH ) amphibole /([Cl]/[OH]) melt ln K Cl = 6.59 K/(Na + [A] □) - 0.679 Mg + 0.487 [6] Fe where X signifies a mole fraction of an anion on the O(3) site; [Cl] and [OH] signify melt mole fractions of the anion in question on a one-oxygen (Stolper-Zhang) basis; K, Na, [A]o, Mg, and [6] Fe signify the amount of each component in the amphibole in atoms per amphibole formula unit, with [A] □ denoting vacancies on the amphibole A site. We then combine the Popp et al. model with our new model to link the occupancy of the amphibole O(3) site and other crystal chemical parameters to the Cl and H 2 O content of melts crystallizing amphibole. The competition between OH and Cl for this site can be used to calculate the melt and amphibole OH/H 2 O contents, as well as the speciation of Fe in amphibole, provided that the Cl content of both the amphibole and its coexisting melt is known, without analyzing either phase for H or Fe 3+ /Fe 2+ . While the models in this paper should be recalibrated using future experimental data, this work shows that considerably more information about the volatile contents of magmas can be gleaned from amphibole than previously shown and provides additional information about the crystal chemistry of amphibole and how it affects Cl partitioning into minerals of this group.

The crystal structure and chemical composition of a crystal of (Mg 1- x Cr x )(Si 1- x Cr x )O 3 perovskite (with x = 0.07) synthesized in the model system Mg 3 Cr 2 Si 3 O 12 -Mg 4 Si 4 O 12 at 23 GPa and 1600 °C have been investigated. The compound was found to be orthorhombic, space group Pbnm , with lattice parameters a = 4.8213(5), b = 4.9368(6), c = 6.9132(8) Å, V = 164.55(3) Å3. The structure was refined to R = 0.046 using 473 independent reflections. Chromium was found to substitute for both Mg at the dodecahedral X site (with a mean bond distance of 2.187 Å) and Si at the octahedral Y site (mean: 1.814 Å), according to the reaction Mg 2+ + Si 4+ = 2Cr 3+ . Such substitutions cause a shortening of the <X-O> and a lengthening of the <Y-O> distances with respect to the values typically observed for pure MgSiO 3 perovskite. Although high Cr-contents are not considered in the pyrolite model, Cr-bearing perovskite may be an important host for chromium in the lower mantle. The successful synthesis of perovskite with high-Cr content and its structural characterization are of key importance because the study of its thermodynamic constants combined with the data on phase relations in the lower-mantle systems can provide new constraints on thermobarometry of perovskite-bearing assemblages.