Volume 95, Issue 5-6

Ultra-high vacuum dynamic scanning force microscopy (dynamic SFM) has been performed on in situ cleaved and as-grown (001) surfaces of low-T, m = 18 and m = 20, antigorite from the Kovdor Mine, Russia. The internal microstructure of the same crystal before cleavage has been checked by conventional TEM on FIB-cut cross-sections. The structural wave is imaged by dynamic SFM with a ~0.25 nm topographic amplitude (outcropping tetrahedral sheet) on cleaved and as-grown surfaces, and with a ~0.5 nm topographic amplitude (outcropping tetrahedral + octahedral sheets) mostly found on cleaved surfaces. Atomic resolution imaging was successfully applied on the cleavage surface through imaging individual atomic features on the outer hexagonal net of the emerging (Mg, O, OH) octahedra of the half-wave. The antigorite cleavage crack undulates through a single octahedral sheet, thereby avoiding rupture of strong Si-O bonds. The two tetrahedral reversals, which form the edges of the modulation repeat, are found to be strongly non-equivalent in structure: across <010>, one reversal is sharp as expected from the standard models of the antigorite structure, whereas the other reversal is unexpectedly “extended.” The latter suggests some scheme of anti-polar positioning of silicate tetrahedra along <010> at the 6-membered ring reversal. High-resolution transmission electron microscopy (HRTEM) structure imaging of antigorite viewed down to <010> confirms spread out electron densities at this reversal. Numerous step height measurements on (001) surfaces show incremental results as integral multiples of 0.25 nm, the spacing between O,OH surfaces along c*. Many of them differ in height from integral multiples of the unit cell repeat along c* and could be explained from carving the bulk wave structure. For all surfaces and steps, local stoichiometry and global electro-neutrality of the surface are satisfied.

The response of the mesolite crystal structure (Na 16 Ca 16 Al 48 Si 72 O 240 ·64H 2 O) to dehydration was evaluated as a function of temperature and partial pressure of water (i.e., P H₂O or relative humidity, RH) using laboratory X-ray powder diffraction (XRD; CuKα radiation) and synchrotron X-ray pair distribution function (PDF) methods. At 425 °C under low-P H₂O conditions (P H₂O ≤ ~1.3 mbar), dehydrated mesolite preserved the long-range ordered aluminosilicate framework structure, which has not been previously observed. This new dehydrated phase, x-metamesolite, has unit-cell parameters [a = 16.731(3) Å, b = 17.822(2) Å, c = 6.312(1) Å, V = 1882.5(5) Å 3 , and possible space group Fdd2] similar to those of other dehydrated natrolite phases (either α1- or α2-metanatrolite). Conversely, under high-P H₂O conditions (P H₂O > ~1.3 mbar), dehydrated mesolite became amorphous (amorphous T 5 O 10 ) at 425 °C. The local structure of amorphous T 5 O 10 was characterized by PDF analyses, which showed the formation of twisted T 5 O 10 nano-fibers [with dimensions (LWH) of ~6.9 × 6.9 × 6.3 Å] resulting from breakage of the mesolite aluminosilicate framework. The two distinct high-temperature P H₂O -dependent phase transition paths illustrate the importance of considering the combined effects of temperature and P H₂O in mesolite. In addition, the low-temperature phase transition in mesolite, involving order-disorder of the extraframework cations, also showed a P H₂O -dependent transition temperature. Although, there is no path dependence on P H₂O for this transition, the local arrangement of Na, Ca, and vacancies in disordered metamesolite (formed through the extraframework cation order-disorder phase transition) likely influences the thermal stability of the aluminosilicate framework during further heating.

Esperite from Franklin, New Jersey, was first described by Moore and Ribbe (1965) as monoclinic with a well-developed “superlattice” a = 2 × 8.814(2) Å, b = 8.270(3) Å, c = 2 × 15.26(1) Å, β ≈ 90°, space group P2 1 /n (subcell), and the chemical formula PbCa 3 (ZnSiO 4 ) 4 . They attributed “superlattice” reflections to the ordered distributions of Pb and Ca cations over four beryllonite-type subcells for esperite with the Ca:Pb ratio greater than 2:1. We examined two esperite fragments from the type sample using single-crystal X-ray diffraction, electron microprobe analysis, and Raman spectroscopy. Although both fragments have Ca:Pb ≈ 1.8, one exhibits the “superlattice” reflections as observed by Moore and Ribbe (1965), whereas the other does not. The sample without “superlattice” reflections has unit-cell parameters a = 8.7889(2), b = 8.2685(2), c = 15.254(3) Å, β = 90.050(1)°, V = 1108.49(4) Å 3 , and the chemical composition Pb 1.00 (Ca 1.86 Fe 2+ 0.07 Mn 0.04 Cr 3+ 0.02 ) Σ=1.99 (Zn 1.00 Si 1.00 O 4 ) 3 . Its crystal structure was solved in space group P2 1 /n (R 1 = 0.022). Esperite is isostructural with beryllonite, NaBePO 4 , and its ideal chemical formula should, therefore, be revised to PbCa 2 (ZnSiO 4 ) 3 , Z = 4. The ZnO 4 and SiO 4 tetrahedra in esperite share corners to form an ordered framework, with Pb 2+ occupying the nine-coordinated site in the large channels and Ca 2+ occupying the two distinct octahedral sites in the small channels. The so-called “superlattice” reflections are attributed to triple twins, a trilling of ~60° rotational twinning around the b axis, similar to those observed in many other beryllonite-type materials. A phase transformation from a high-temperature polymorph to the esperite structure is proposed to be responsible for the twinning formation.

In this paper, I demonstrate that the complex structure observed in natural dendritic zircon, which crystallized from a mafic magma, can be approximated by a simple model of deterministic volumefilling fractal growth. The model comprises a novel dendritic growth process that reveals a previously unrecognized underlying structure to complex dendritic crystals, and provides an ideal way of maximizing surface area at the crystal-melt interface during dendritic crystal growth. This addresses the important kinetic effect of creating interfacial area. In turn, this relates to dissipation of the latent heat of fusion from the moving crystal-melt interface, which, in addition to chemical diffusion, is known to be a fundamental rate-controlling process in dendritic crystal growth. A new mechanism of tip-splitting branch formation in dendritic crystals is proposed. Although both types of branch formation seem to occur simultaneously, the newly proposed mechanism operates at larger length scales and independently of classical side-branching linked with periodic perturbations caused by thermal noise. It is shown that this type of modeling potentially has applications in metallurgical engineering; and in predicting the relative lengths, orientations, and spacings of branches in mathematical modeling studies of natural and experimentally grown dendritic crystals.

Binary iron sulfides are of major interest and importance in environmental, geological, and planetary science. Oxidative high-temperature oxide melt drop-solution calorimetry in molten sodium molybdate (3Na 2 O·4MoO 3 ) solvent at 975 K was applied to determine the energetics of formation of the binary iron monosulfide solid solution (pyrrhotite) (Fe 1-0.125x S, 0 ≤ x ≤ 1). The enthalpies of formation from elements are consistent with earlier data in the literature, available for a few compositions. Within the experimental errors, the enthalpies of formation of the solid solution from the end-members Fe 0.875 S and FeS (ΔH mix , kJ/mol) at 25 °C equal to zero. Under the assumption of random distribution of Fe vacancies, the Gibbs free energies of mixing of Fe 1-0.125x S (0 ≤ x ≤ 1) are estimated. Our data support the two-sublattice model proposed by Waldner and Pelton (2005).

Crystals of the solid-solution series of (Ca,Sr)-lawsonite were synthesized hydrothermally at 4 GPa and 600 and 800 °C in piston-cylinder experiments. Synthesis products were analyzed with SEM, EMP, and powder-XRD. Lawsonite was observed in both the orthorhombic space group Cmcm and in the monoclinic space group P2 1 /m. It is exclusively orthorhombic at low x Sr bulk but monoclinic at high x Sr bulk ; in the range x Sr bulk = 0.18 to 0.4 both polymorphs coexist and the data suggest a two-phase field between x Sr ortho ~0.1-0.2 and x Sr mono ~0.3-0.4 at 4 GPa/600 °C. Linear regression to the refined lattice parameters yields a = 0.017·x Sr + 5.841 (Å), b = 0.197·x Sr + 8.787 (Å), c = 0.263·x Sr + 13.130 (Å), and v = 4.62·x Sr + 101.46 (cm 3 /mol) for orthorhombic lawsonite and a = 0.119·xSr + 5.306 (Å), b = 0.118·x Sr + 13.160 (Å), c = 0.025·x Sr + 5.833 (Å), β = 0.38·x Sr + 124.07 (°), and v = 3.20·x Sr + 101.59 (cm 3 /mol) for monoclinic lawsonite. The data suggest an increasingly negative Δv ortho-mono with increasing x Sr . In monoclinic lawsonite, structural expansion due to the incorporation of Sr is primarily accomplished by tilting and rotation within the Si 2 O 7 -group, whereas in orthorhombic lawsonite this tilting and rotation is prohibited by symmetry restrictions and expansion is mostly accomplished by an increase in lattice parameters. Combining the extrapolated Ca end-member volume for monoclinic lawsonite with published high-P data yields K 0 mono = 137(3) GPa (K′ = 4.4). Contrary to the Ca end-member system, the Cmcm-P2 1 /m phase transition is quenchable within the Sr-bearing system. A tentative phase diagram for (Ca,Sr)-lawsonite at 600 °C indicates a narrow orthorhombic-monoclinic two-phase field that shifts significantly to lower pressure with increasing x Sr . The Cmcm-P2 1 /m phase transition in the Sr end-member system is located at ≤1 GPa at ~400 to 600 °C, 6 to 9 GPa below the transition in the Ca-system, and has a negative P-T slope.

Coulsellite, CaNa 3 AlMg 3 F 14 , from the Cleveland tin mine at Luina, western Tasmania, has a rhombohedral distortion of the cubic pyrochlore A 2 B 2 X 6 Y structure, with a = 7.1756(1) Å, α = 59.867(1)°, space group R3̄m, Z = 1. The corresponding hexagonal cell parameters are a = 7.1620(1) Å, c = 17.5972(3) Å. The crystals are multiply twinned about threefold axes of the pseudocubic cell. The structure was determined using X-ray data collected on a twinned crystal and refined to R obs = 0.027 for 452 observed reflections with I > 2σ(I). The structure is possibly unique among published structures of pyrochlore-like minerals in having full 1:3 ordering of Ca:Na in the A sites and Al:Mg in the B sites. Transmission electron photomicrographs show a nanodomain structure due to twinning on a scale of ~5 nm.

Natural kaolin, from Fujian province in China, was used as raw material to synthesize zeolite 4A powder under low-temperature hydrothermal treatment in alkali solution. Optimization studies on various reaction parameters were conducted. With the addition of an inorganic binder (montmorillonite), the as-prepared powder was shaped into spheres for desiccant application in industrial fields. Zeolite 4A powder was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the obtained powder was a cubic phase with high crystallinity. The water sorption capacity (WSC) and final compression strength (FCS) of zeolite 4A desiccant were studied. Higher crystallinity of zeolite 4A powder led to the higher WSC of zeolite desiccant. The observed WSC and FCS of 21.0% and 44.8 N, respectively, confirmed the potential application of zeolite 4A for water sorption

Single crystals of hydrous ferroan ringwoodites with compositions (Mg 0.97 Fe 1.00 ) 1.97 Si 0.98 H 0.13 O 4 and (Mg 1.21 Fe 2+ 0.66 Fe 3+ 0.1 ) 1.97 Si 0.97 H 0.06 O 4 have been synthesized. Their lattice parameters at ambient conditions are a = 8.1597(6) Å and V = 543.28(13) Å 3 and a = 8.1384(3) Å and V = 539.03(7) Å 3 , respectively. The unit-cell lattice parameters were measured at different pressures up to about 9 GPa by means of X-ray single-crystal diffraction. The P-V data were fitted with a second-order Birch-Murnaghan equation of state (K′ fixed to the value of 4) refining to the following equation of state parameters: V 0 = 543.32(7) ų and K T0 = 186.5(9) GPa for (Mg 0.97 Fe 1.00 ) 1.97 Si 0.98 H 0.13 O 4 and V 0 = 539.01(5) ų and K T0 = 184.1(7) GPa for (Mg 1.21 Fe 2+ 0.66 Fe 3+ 0.1 ) 1.97 Si 0.97 H 0.06 O 4 . Structural refinements indicate the presence of significant octahedral vacancies in sample (Mg 1.21 Fe 2+ 0.66 Fe 3+ 0.1 ) 1.97 Si 0.97 H 0.06 O 4 due to the oxidation of 0.1 apfu of ferric iron. Correlation between the O-O distances of the octahedral edges and the shift of the OH-stretching frequency suggest that the H incorporation occurs at the octahedral site.

Kapundaite, ideally (Na,Ca) 2 Fe 4 3+ (PO 4 ) 4 (OH) 3 ∙5H 2 O, is a new mineral (IMA2009-047) from Toms phosphate quarry, Kapunda, South Australia, Australia. The new mineral occurs as cavernous aggregates of fibers up to several centimeters across, associated with leucophosphite, natrodufrenite, and meurigite-Na crystals and amorphous brown, black, and/or greenish coatings. Individual kapundaite crystals are very thin flattened fibers up to a few millimeters in length, but typically no more than a few micrometers in thickness. The main form observed is {100}; other forms in the [010] zone are present, but cannot be measured. Crystals of kapundaite are pale to golden yellow, transparent to translucent, have a yellow streak and silky luster, and are non-fluorescent. Mohs hardness is estimated to be about 3; no twinning or cleavage was observed. Kapundaite is biaxial (+), with indices of refraction α = 1.717(3), β = 1.737(3), and γ = 1.790(3). 2V could not be measured; 2V calc is 64.7°. The optical orientation is Z = b, Y ≈ c with weak pleochroism: X = nearly colorless, Y = light brown, Z = pale brown; absorption: Y > Z > X. No dispersion was observed. The empirical chemical formula (mean of seven electron microprobe analyses) calculated on the basis of 24 O is (Ca 1.13 Na 0.95 ) Σ2.08 (Fe 3+ 3.83 Mn 0.03 Al 0.02 Mg 0.01 ) Σ3.89 P 3.92 O 16 (OH) 3 ·5H 2.11 O. Kapundaite is triclinic, space group P1, a = 6.317(5), b = 7.698(6), c = 9.768(7) Å, α = 105.53(1)°, β = 99.24(2)°, γ = 90.09(2)°, V = 451.2(6) Å 3 , and Z = 1. The five strongest lines in the powder X-ray diffraction pattern are [d obs in Å (I) (hkl)]: 9.338 (100) (001), 2.753 (64) (21̄1), 5.173 (52) (011), 2.417 (48) (2̄1̄3, 202, 01̄4), and 3.828 (45) (02̄1). The crystal structure was solved from single-crystal X-ray diffraction data using synchrotron radiation and refined to R 1 = 0.1382 on the basis of 816 unique reflections with Fo > 4σF. The structure of kapundaite is based on a unique corrugated octahedral-tetrahedral sheet, which is composed of two types of chains parallel to a. Kapundaite is structurally related to mélonjosephite. The mineral is named for the nearest town to the quarry.

A mixture of antigorite, forsterite, and enstatite was reacted at 2 GPa pressure, with water, to study kinetics of the reaction Mg 48 Si 34 O 85 (OH) 62 = 10 Mg 2 Si 2 O 6 + 14 Mg 2 SiO 4 + 31 H 2 O. Reaction progress, F, which can vary between +1 and -1, was measured by comparing areas under X-ray diffraction peaks for run products with corresponding peaks for the starting material. Rates for dehydration and hydration can be regressed with the equation: The function F R accounts for the decrease in A θ , specific surface area, from A θ ° at F = 0 to 0 at F = 1: where p, ~0.50 for elongate grains, characterizes grain shape. Regression of the rate equation for dehydration runs can be combined with A θ °, measured on the antigorite starting material, to give reaction rate Kr: -9.2(1.2) × 10 -15 mol/s/cm 2 . With that rate, we calculate that well-defined conventional reversal brackets of 5 °C around the equilibrium temperature would require run lengths of 729(99) h, considerably longer than in this or any previous study. The rate equations can be applied to the question of overstepping of antigorite dehydration below arcs. One modeled geotherm 40 km below a slab surface crosses the antigorite dehydration reaction at about 2 GPa; the slab takes 3 × 10 5 years to warm one degree. For grain sizes in a serpentinite in the 0.1 to 10 cm range, complete dehydration would take 10 4 -10 5 years. During that time, the plate would travel no more than a kilometer past the point of first dehydration. If earthquakes associated with dehydration occurred on timescales of 10 3 -10 4 years, complete dehydration of a volume of plate would require 10-100 separate dehydration events.

Infrared spectroscopic quantification of traces of OH and H 2 O in minerals and glasses is based on the Beer Lambert law A = ε·c·t, where ε is the molar absorption coefficient. Numerous experimental and theoretical studies show that ε generally increases with decreasing wavenumbers. However, this general trend seems to be valid only for hydrous minerals and glasses and should not be applied to water quantification in nominally anhydrous minerals (NAMs) that incorporate traces of water in their structures. In this study, we analyze ε-values from literature data and propose that within a polymorphic mineral series of the same composition ε negatively correlates with the molar volume and positively correlates with the density of the respective mineral phase. To test this hypothesis, we determined ε-values for synthetic hydrous ringwoodite samples ranging in composition from X Mg = 0.0 to 0.6 by combining results of FTIR-spectroscopy with those of secondary ion mass spectrometry. The ε-values plot well below the general calibration curves but follow the same trend, i.e., they increase with decreasing wavenumbers of the OH bands from 59 000 ± 6000 for the Fe end-member to 85 800 ± 10 000 L/mol(H 2 O)/cm -2 for the Mg-richest sample. From this relation we can predict an absorption coefficient for the iron-free Mg end-member as 100 000 ± 7000 L/mol(H 2 O)/cm -2 . This value together with ε-values for forsterite and wadsleyite taken from literature confirm the proposed correlation with the molar volume and density within this polymorphic series. This allows us to predict absorption coefficients for some minerals, where coefficients for one or better two of their polymorphs, either high- or low-pressure, are available.

The reactivity, oxygen fugacity, volatility, and wetting properties of tin complicate experimental work in tin-bearing systems. Open-graphite and vitreous-carbon crucibles may be used for preparing tin-rich glass starting materials. Such glasses are prepared by fusing mixtures of stannous oxalate with oxides, crushed rocks, or silicate gels. Decomposition of SnC 2 O 4 into CO+CO 2 and SnO provides a reducing atmosphere for the incorporation of Sn +2 into the silicate melt, while Sn +2 provides an effective flux. Such melts can incorporate Sn far in excess of any reasonable abundance of this element in natural silicate magmas. Experiments where constant bulk composition is required are best conducted in sealed crucibles because SnO is lost as gas. Evacuated silica tubes may be used for such purposes if saturation in SiO 2 is desired; however, oxygen fugacity cannot be independently controlled. Rhenium metal is a useful crucible material for relatively reduced Sn-bearing experiments (below oxidation to ReO 2 ), and the coexistence of metallic Sn and stannic oxide controls oxygen fugacity. Adverse mechanical properties inherent to Re, such as work-hardening and embrittlement, are addressed by the use of thick-walled capsules in the piston-cylinder apparatus. Such capsules behave elastically at temperatures of geological interest (~1100 °C), producing higher sample pressures than those provided by the surrounding solid media. These high sample pressures are found to partially relax in week-long experiments. Sealed graphite, sintered SnO 2 , and Re-foil capsules are plausible crucible materials for Sn-bearing experiments, but may only be used if their porosity and brittleness can be moderated

Anhydrous minimum-melting equilibria saturated with SnO 2 form a pseudo-binary within Sn- SnO 2 -SiO 2 close to the join SnO-SiO 2 . This relationship, previously observed in various studies at 1 atmosphere and confirmed here, is explored more uniformly across the full compositional range of the system at pressure of ca. 10 kbars using Re capsules. Eutectic points and curves increase significantly in temperature with 10-11.6 kbars of pressure with only modest shifts of eutectic composition from that at ca. 1 bar pressure. No silicate liquid immiscibility was encountered in the minimum-melting regime although it may develop with increasing pressure in SiO 2 -rich compositions. Possible configurations for the equilibria at temperatures greater than minimum melting suggest wide fields of Sn-SiO 2 and SnO 2 -SiO 2 liquid immiscibility on either side of the SnO-SiO 2 join. The SnO-SiO 2 pseudo-binary involves a trough between the two thermo-compositional immiscibility maxima that reflects the thermal stability and volatility of the SnO dimer and its complexes. In general, these data support high solubility of tin in anhydrous silicate melts, at geologically relevant temperatures and somewhat low oxygen fugacities, as the tin contents of the run products ranged from 24-62 and 51-81 wt%, respectively, for ca. 1 bar and 10 kbar experiments.

Carbonate-talc altered ultramafic (and mafic) rocks of the obducted oceanic lithosphere along the Main Mantle Thrust in the Swat Valley host emerald deposits and are invaded by quartz veins and stockworks. Both the quartz veins and carbonate-talc altered rocks contain discrete grains and clusters of tourmaline crystals, which may be associated with emerald and/or chromian muscovite. Tourmalines from the Mingora and Gujar Kili emerald mines and the Spin Obo-Kuh area are Nibearing, Cr-rich dravites and “oxy-dravites” that exhibit substantial chemical variability with 2.0-2.5 atoms per formula unit (apfu) Mg, relatively low Al (4.8-5.8 apfu), high Cr (0.5-1.8 apfu), high Cr/(Cr+Al) ratios of 0.08-0.28, significant amounts of Ni (up to 0.11 apfu), and variable calculated W site O 2- (0.2-0.8 apfu). The mechanisms that appear to control the tourmaline chemistry at these localites are combinations of the dominant substitution Al = Cr with lesser amounts of the Mg+OH 1- = (Al,Cr)+O 2- and Al 3+ = Fe 3+ substitutions. Relative to the Mingora, Gujar Kili, and Spin Obo-Kuh areas, the Charbagh tourmalines are “oxy-dravites” that have comparable Mg contents (2.2-2.3 apfu) with variable calculated W site O 2- (0.6-0.9 apfu), but are more Fe-rich (0.5 apfu) and Al-rich (6.0-6.3 apfu) with low Cr (0.00-0.01 apfu) and Ni contents (0.01-0.02 apfu). The mechanism that appears to control the variable chemistry of the Charbagh tourmalines is primarily Mg+OH 1- = Al+O 2- . The chemical characteristics of tourmalines from the various localities relate most clearly to differences in host rock chemistry. Tourmalines from the carbonate-talc altered ultramafic-mafic rocks and the invasive quartz veins have a common hydrothermal origin associated with emplacement and crystallization of younger granitoids. Furthermore, the occurrence of Swat emeralds in quartz-tourmaline (±chromian muscovite) veins suggests that the tourmaline is cogenetic with emerald formation. The quality and quantity of Swat emeralds depend on the: (1) host rock composition and (2) nature of the hydrothermal fluids. Large deposits of gem-quality emerald occur in carbonate-altered ultramafic rocks, which also contain Cr-rich dravites and “oxy-dravites.” This suggests that the presence of high-Cr magnesian tourmalines, particularly in magnesite-talc altered ultramafic rocks, can represent a criterion for further emerald exploration in the lower Swat region of Pakistan and comparable ultramafic-hosted emerald-producing regions.

Droplets of an iron-bearing calcia magnesia aluminosilicate (Fe-CMAS) melt were reacted under distinctly reducing conditions (f O₂ = 2.4 × 10 -13 and 6.4 × 10 -15 atm) at high temperature (~1400 °C) and ambient pressure. The low f O₂ environment was maintained by a flowing gas mixture of CO and CO 2 , with a high content of CO. Molten metallic iron alloyed with silicon and carbon formed on the surface of the melt; no metal was observed in sample interiors. A color change from brown to pale blue confined to the outer layer of the melt indicated that essentially complete reduction of Fe 3+ to Fe 2+ had occurred in this region. Analysis of the reaction kinetics, particularly in comparison to melts of similar polymerization but free of CaO, reveals that the concentration of electron holes has decreased to such an extent that ionic transport in the melt is significantly slowed and the diffusion of CO as a neutral species becomes dominant and rate-limiting: molecular CO, initially incorporated into the melt as a physically dissolved species, subsequently reacts to form chemically dissolved (bonded into the melt structure) CO 3 2- anions, consuming electron holes in the process. The chemical diffusion coefficient for CO in the reduced melt at 1400 °C is estimated as D CO ≈ 4 × 10 -4 cm 2 /s, consistent with that of other, similarly sized molecular species (e.g., H 2 and H 2 O) for similarly polymerized melts, as reported by other investigators. Upon quenching, the droplet acts as a closed system. Internal redox couples see the reduction of the carbonate so as to form bubbles of CO, the composition of which are confirmed with Raman spectroscopy. The open-system reduction and closed-system quenching dynamics are analyzed following an Ellingham-diagram approach.

Chrysotile [Mg 3 Si 2 O 5 (OH) 4 ] and tremolite [Ca 2 Mg 5 Si 8 O 22 (OH) 2 ] asbestos represent two distinct mineralogical categories of regulated asbestos commonly evaluated in epidemiological, toxicological, and pathological studies. Human respiratory and gastric systems are sites of asbestos deposition where chrysotile and tremolite asbestos are undersaturated with respect to biological fluids and dissolution kinetics control the persistence of these minerals in biological environments. Here we examined the biodurabilities (i.e., the resistance to dissolution) of chrysotile and tremolite asbestos in simulated body fluids as a function of mineral surface area over time. Batch experiments in simulated gastric fluid (SGF; HCl and NaCl solution at pH 1.2) and simulated lung fluid (SLF; modified Gamble’s solution at pH 7.4) were performed at 37 °C over 720 h to evaluate the dissolution of chrysotile vs. tremolite asbestos in acidic and near-neutral biological fluids. The rate-limiting step of Si release for both minerals was used to obtain rate constants (k) and reaction orders (n) allowing comparisons of mineral dissolution rates. Both chrysotile and tremolite asbestos are less biodurable in SGF (low pH) compared to SLF (near-neutral pH). Based on equivalent surface area comparisons, the surface chemistry of tremolite is more reactive in lung fluid than chrysotile and vice versa in digestive fluid. However, the relative biodurabilities of these asbestos silicates (from most to least) are tremolite (SLF) > chrysotile (SLF) > tremolite (SGF) > chrysotile (SGF) when accounting for the greater surface area of chrysotile per mass or per fiber compared to tremolite. Overall, this study illustrates the importance of surface area and fiber morphology considerations when evaluating the biodurabilities of asbestiform minerals.

Two C2/c pyroxenes, CaMnSi 2 O 6 and CaZnSi 2 O 6 , were investigated at high pressure by singlecrystal X-ray diffraction. Their unit-cell parameters were determined at 9 different pressures up to 7.55 and 8.23 GPa, respectively. No evidence of phase transformations was found for either sample throughout the investigated pressure range. The pressure-volume data were fit using a third-order Birch-Murnaghan equation of state and it was possible to refine simultaneously the unit-cell volume V 0 , the bulk modulus K T0 and its first pressure derivative K′ providing the following coefficients: V 0 = 462.01(3) Å 3 , K T0 = 97.3(4) GPa, K′ = 7.5(2) for CaMnSi 2 O 6 and V 0 = 444.79(2) Å 3 , K T0 = 109.6(5) GPa, K′ = 7.0(2) for CaZnSi 2 O 6 . The substitution of Zn for Mn at the M1 crystallographic site causes a strong decrease of the bulk modulus (by about 11%). Intensity data were collected at several pressures for both samples. The main compression mechanism is related to the tetrahedral chain kinking and the consequent shortening of the Ca-O3 long bond distances, which show a markedly larger decrease for the CaMnSi 2 O 6 sample. Comparing the results obtained in this work with previous data for Ca/ Na-bearing C2/c pyroxenes containing trivalent and divalent 3d-transition elements at M1 site, we identified two distinct compressibility trends: for a similar unit-cell volume at room pressure the pyroxenes with Na on M2 and trivalent cations on M1 are more compressible than those having Ca on M2 and divalent cations at the M1 site. The analysis of the structure evolution for all samples indicates that this is strongly correlated with the evolution of kinking of the tetrahedral chains and the shortening of the M2-O3 bonds.

EPMA analyses of uvarovite from the chromite-bearing ultramafic intrusive of Sukinda, India, show that uvarovite containing 9.83 to 17.68 wt% Cr 2 O 3 represents a solid solution of the binary uvarovite-andradite series with Uva 34-58 And 42-58 . Associated chromite grains with 57-59 wt% Cr 2 O 3 do not show any compositional variation from core to rim. 57 Fe Mössbauer spectroscopic studies on the uvarovite samples undertaken both at room temperature (298 K) and low temperature (110 K) indicate the presence of Fe 3+ only in octahedral coordination. Uvarovite grew from chromite (Cr source) and pyroxenes (Al, Fe, and Ca source) of the ultramafic host rocks.

Compounds of the Na 2 (Mn 1-x M 2+ x )Fe 2+ Fe 3+ (PO 4 ) 3 (M 2+ = Mg, Cd, Ca, Ni, Zn) alluaudite-type solid solutions were synthesized by hydrothermal techniques at 1 kbar, between 400 and 600 °C, and were investigated by X-ray powder diffraction and infrared spectroscopy. The site occupancy factors of the Na 2 (Mn 1-x Cd x )Fe 2+ Fe 3+ (PO 4 ) 3 compounds, obtained from the Rietveld refinements of the X-ray powder patterns, indicate that the replacement of Mn by Cd mainly takes place on the M1 site. Small amounts of Cd were also detected on the A1 site, compensated by small amounts of Na occurring on M1. The cationic distributions in the Na 2 (Mn 1-x Mg x )Fe 2+ Fe 3+ (PO 4 ) 3 solid solution show a partially disordered distribution of Fe and Mg over the M1 and M2 crystallographic sites. The unit-cell parameters increase significantly when Mn is replaced by Ca or Cd, and decrease significantly when it is replaced by Ni, Mg, or Zn. The infrared spectra show the displacement of two absorption band at ca. 405-445 cm -1 and 595-610 cm -1 , which are assigned to the vibrations of the M 2+ cations localized on the M1 and M2 sites, respectively. This assignment is confirmed by the excellent correlations between the average ionic radius of the cations occurring on the M sites, and the energy of the absorption band.

The Gibbs free energy change, ΔG r , dependence of the anorthite dissolution rate in a supercritical CO 2 -water system was measured as part of a geochemical assessment of CO 2 geological sequestration. Being bounded at ΔG r crit , the critical ΔG r required for an opening of the etch pit at a screw dislocation, it has been accepted that mineral dissolution follows etch pit formation assisted by dislocations below ΔG r crit , whereas the horizontal step retreats without the etch pit above ΔG r crit . The experiment described herein, however, revealed that another mode of dissolution occurs more distant from equilibrium by spontaneous formation of the etch pit over the entire surface, as observed on calcite. The dissolution rate is higher by more than one order of magnitude than that in the dislocation-assisted mode. Therefore, including the rate gap at ΔG r crit , a nonlinear curve with three steps instead of a sigmoidal curve is proposed for the ΔG r dependence of the anorthite dissolution rate. Extremely slow rates were observed depending on observed points for the same ΔG r condition. Although the reason for such a rate difference remains unknown, it is likely related to the defect density on the crystal surface. It is possible that initial spreading of the dissolved surface attributable to the etch pit formation assisted by defects provides some trigger for subsequent explosive etch pit formation. These findings suggest that the initial transient process can strongly influence the kinetics of geochemical reactions that occur during CO 2 geological sequestration.

Nanoindentation experiments were conducted to investigate the elasticity normal to the basal plane of six non-expandable, hydrous 2:1 phyllosilicate minerals (pyrophyllite, talc, biotite, two muscovite samples, and margarite) with layer charge z ranging from 0 to 1.823 per O 10 (OH) 2 . For the examined indentation depth h of ≤200 nm, the measured Young’s modulus E decreases with increasing h. Furthermore, the rate of reduction in the apparent E, in general, decreases with increasing z. The dependence of apparent E on h is attributed to indentation-induced inelastic deformation, particularly the deformation related to the high local stresses beneath the indenter tip, such as kink band formation, layer delamination, void generation, and cracking, which tend to cause damage to the layer structure. To minimize the influence of inelastic deformation on the measurement of E by indentation, the maximum E at small h is proposed to be the truly representative elastic modulus. The stiffest species, margarite, with z = 1.823, has a representative E of 165.5 GPa, seven times greater than that of pyrophyllite with z = 0 and E = 23.5 GPa. A nearly linear correlation between the representative E and the square of the ratio of the surface charge density σ to half of the basal spacing d(001), [2σ/d(001)] 2 , exists. This relationship suggests that the elasticity normal to the basal plane of these phyllosilicates is primarily controlled by the long-range electrostatic attractions between the 2:1 layer and interlayer cations instead of atomic bonds within the 2:1 layer, although other compositional and structural variations also affect the interlayer interactions. This relationship may indicate that the interlayer complexes can be used as the elasticity signatures of phyllosilicate minerals.

We report the pressure dependence of the Mössbauer spectra and the electrical resistivity up to 9.1 GPa at room temperature for a native iron sample collected from the Precambrian Chaibasa shales, Singhbhum Craton, Eastern India. The Mössbauer spectroscopy of the sample at ambient conditions yields isomer shifts and magnetic hyperfine field values that confirm the presence of Fe 0 oxidation state. Many theories have been put forward to explain the origin of this native iron including a Precambrian meteoritic impact. High-pressure Mössbauer spectroscopic measurements using diamond anvil cell (DAC) showed a constant isomer shift up to 5.6 GPa with a subtle variation of -1.07 × 10 -3 mm/s/GPa followed by sharper change -4.3 × 10 -3 mm/s/GPa above 6.3 GPa, a pressure much lower than the usual value reported for metallic iron. Further increase of pressure to 9.1 GPa results in the emergence of a tiny peak at ~0 isomer shift indicating the onset of the martensitic phase transition of iron from the body-centered-cubic (bcc) to hexagonal-close-packed (hcp) transition 4 GPa lower than the transition pressure normally observed for pure iron. This phase transition in the native iron is confirmed by high-pressure electrical resistivity study. Lowering of the transition pressure could be due to nucleation of hcp by stacking faults caused by shock metamorphism resulting from the Precambrian impact in the region.

Paraspurrite is discredited as a mineral species. No type material was available necessitating collecting new material from the original locality. A crystallographic study shows paraspurrite to be polysynthetically twinned spurrite, twin law by reflection on {001}. The spurrite cell calculated from XRPD unit-cell refinement is a = 10.478(3), b = 6.700(2), c = 14.127(3) Å, β = 101.02(2)°, V = 972.8(3) Å 3 . The cell refined on two “twinned” crystals yielded: a = 10.494(1), b = 6.7116(6), c = 28.216(3) Å, α = 90.059(6), β = 100.132(5), γ = 90.023(6)°. This monoclinic primitive cell transforms to monoclinic B (Fig. 2): a = 10.494, b = 6.7116, c = 55.56 Å, α = 90, β = 90.6, γ = 90°, which corresponds to a sub-cell described as “paraspurrite” by Colville and Colville (1977); space group P2 1 /a with cell parameters: a = 10.473, b = 6.706, c = 27.78 Å, α = 90, β = 90.58, γ = 90°. The discreditation has been approved by the IMA Commission on New Minerals, Nomenclature and Classification.

High-pressure experiments and ab initio calculations on the hexagonal close-packed (hcp) structure of pure iron were performed to investigate a pressure-induced magnetic transition and the equation of state in the pressure range of 0-107 and 0-400 GPa, respectively. The experimental data at room temperature showed a significant change in the cell parameter ratio at 55 GPa without any major structural changes occurring. Ab initio calculations at 0 K indicate that the change in the cell parameter ratio observed in the high-pressure experiments corresponds to a magnetic transition from an antiferromagnetic state to a nonmagnetic state. If the hcp-Fe is stable under inner core conditions, then the density of nonmagnetic hcp-Fe is ~6% denser than that of the inner core, as determined using the PREM model. This supports the view that the composition of the inner core should be composed of iron and a significant amount of lighter elements.

Synchrotron X-ray fluorescence (SXRF) and X-ray absorption spectroscopy (XAS) have become standard tools to measure element concentration, distribution at micrometer- to nanometer-scale, and speciation (e.g., nature of host phase; oxidation state) in inhomogeneous geomaterials. The new Maia X-ray detector system provides a quantum leap for the method in terms of data acquisition rate. It is now possible to rapidly collect fully quantitative maps of the distribution of major and trace elements at micrometer spatial resolution over areas as large as 1 × 5 cm 2 . Fast data acquisition rates also open the way to X-ray absorption near-edge structure (XANES) imaging, in which spectroscopic information is available at each pixel in the map. These capabilities are critical for studying inhomogeneous Earth materials. Using a 96-element prototype Maia detector, we imaged thin sections of an oxidized pisolitic regolith (2 × 4.5 mm 2 at 2.5 × 2.5 μm 2 pixel size) and a metamorphosed, sedimentary exhalative Mn-Fe ore (3.3 × 4 mm 2 at 1.25 × 5 μm 2 ). In both cases, As K-edge XANES imaging reveals localized occurrence of reduced As in parts of these oxidized samples, which would have been difficult to recognize using traditional approaches.

Single crystals of pure enstatite (Mg 2 Si 2 O 6 ) were synthesized under water-saturated conditions at 6 GPa and 1250 °C and variable silica activity. Run products were investigated using a novel technology: a FTIR spectrometer equipped with a focal plane array detector enabling IR-imaging with a spatial pixel resolution of 2.7 μm. IR spectra within the OH-absorption region show strong pleochroic behavior: absorption bands at 3687 and 3592 cm -1 show strongest absorptions for E||n β , whereas absorption bands at 3362 and 3067 cm -1 show strongest absorptions for E||n γ . Furthermore, absorption bands are sensitive to the silica activity-the ratio of the integral absorbance of the absorption bands at 3687 and 3592 cm -1 to the absorption bands at 3362 and 3067 cm -1 increases with increasing Mg/Si-ratio of the bulk charge. The most probable interpretation is an assignment of the high-energy absorption bands to tetrahedral (T-site) defects caused by a lower availability of Si and the low-energy absorption bands to octahedral (M-site) defects caused by a lower availability of Mg. All crystals show an internal zonation pattern with an increasing T-site to M-site defect ratio from core to rim, which is interpreted to be caused by changing silica-activity and T during the experiments. The defect ratio and the zonation pattern are applied as a monitor of crystal growth conditions.

Akaogiite, an ultra-dense polymorph of TiO 2 was encountered in heavily shocked garnet-cordieritesillimanite gneiss in the Suevite breccia of the Ries meteorite impact crater in Germany. The chemical formula of akaogiite is TiO 2 , containing (wt%) TiO 2 97.6-97.7; Nb 2 O 5 0.15-0.20, and FeO 0.11-0.14. The empirical formula is: Ti 0.998 Fe 0.002 Nb 0.001 O 2 . Akaogiite is optically distinguishable from rutile only in reflected light microscopy, through its slightly higher brightness and the intense royal blue color of its internal reflections in crossed nicols. The mineral grains consist of countless randomly oriented submicrometer particles. In situ micro-beam X-ray diffraction established akaogiite to be monoclinic with the baddeleyite-type structure. Cell parameters are a = 4.606(2) Å, b = 4.896(3) Å, c = 4.933(3) Å, and β = 99.17(6)°; space group P2 1 /c; molar volume = 16.82(2) cm 3 /mol; density = 4.72 g/cm 3 . Akaogiite coexists in the shocked gneiss with graphite-diamond phase transition assemblage, a second dense TiO 2 polymorph with the scrutinyite-type structure (TiO 2 -II), liquidus idiomorphic jadeite inclusions in melt pockets in garnet, and a new FeTiO 3 -polymorph with the Li-niobate structure. The high-pressure assemblage constrains the equilibrium peak-shock pressure to be ≤22 GPa and a post-shock temperature <500 °C, thus correcting previous estimates. The name was approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2007-058). The name is for Masaki Akaogi, Professor at the Department of Chemistry, Gakushuin University in Tokyo, Japan.