Band 95, Heft 2-3

Brownleeite, ideally stoichiometric MnSi, is a manganese silicide not previously observed in nature that was discovered within an interplanetary dust particle that likely originated from a comet. Three submicrometer brownleeite grains were found, with one of them poikilitically enclosed by Mnbearing forsterite. Owing to the small size of the brownleeite grains, it was not possible to determine conventional macroscopic properties of this mineral; however, the chemical composition and crystal structure were well constrained by extensive quantitative energy dispersive X-ray analysis and electron diffraction using transmission electron microscopy (TEM). The crystal system for brownleeite is cubic (a = 4.557 Å) with space group P2 1 3, cell volume = 94.63 Å 3 , Z = 4, density (calculated) = 2.913 g/cm 3 , and empirical formula: (Mn 0.77 Fe 0.18 Cr 0.05 )Si. These brownleeite grains likely formed as high-temperature condensates either in the early Solar System or in the outflow of an evolved star or supernova explosion.

Solid solutions among zircon (ZrSiO 4 , I4 1 /amd) and zircon-structured orthosilicates ASiO 4 (A = Hf, Th, U, Pu, or Ce) are important to a wide variety of applications: nuclear materials, geochronology, and even electronic materials. The thermodynamic mixing properties of the following seven binary solid solutions were simulated using density functional theory followed by Monte Carlo modeling and thermodynamic integration: (Zr,Hf)SiO 4 , (Zr,Th)SiO 4 , (Zr,U)SiO 4 , (Zr,Pu)SiO 4 , (Zr,Ce)SiO 4 , (Hf,Pu) SiO 4 , and (Th,U)SiO 4 . ZrSiO 4 and HfSiO 4 were found to form a nearly ideal solid solution, but the miscibility of the other solid solutions was limited to no more than 12 mol% of the substituting cation. The binaries were ranked by extent of miscibility: (Zr,Hf)SiO 4 > (Th,U)SiO 4 > (Zr,Pu)SiO 4 > (Zr,Ce) SiO 4 > (Hf,Pu)SiO 4 > (Zr,U)SiO 4 > (Zr,Th)SiO 4 . The extent of solid solution has been estimated for each binary. The end-members PuSiO 4 , CeSiO 4 , and USiO 4 were determined to be unstable relative to a mixture of SiO 2(quartz) and crystalline PuO 2 , CeO 2(cerianite) , or UO 2(uraninite) . Isostructural thorite (ThSiO 4 ) is calculated to be marginally stable, but its monoclinic polymorph, huttonite, which has the structure of monazite, is marginally unstable relative to SiO 2(quartz) and ThO 2(thorianite) at 0 K. If thermodynamic equilibrium could be reached at low temperatures, exsolution textures would appear in most zircon solid solutions perpendicular to [001], but perpendicular to a linear combination of [100] and [010] in (Hf,Pu)SiO 4 .

Biominerals can achieve complex shapes as aggregates of crystalline building blocks. In the red coral skeleton, we observe that these building blocks are arranged into eight hierarchical levels of similarly (but not identically) oriented modules. The modules in each hierarchical level assemble into larger units that comprise the next higher level of the hierarchy, and consist themselves of smaller, oriented modules. EBSD and TEM studies show that the degree of crystallographic misorientation between the building blocks decreases with decreasing module size. We observe this organization down to a few nanometers. Thus, the transition from imperfect crystallographic order at millimeter scale to nearly perfect single crystalline domains at nanometer scale is progressive. The concept of “mesocrystal” involves the three-dimensional crystallographic organization of nanoparticles into a highly ordered mesostructure. We add to this concept the notion of “multilevel modularity.” This modularity has potential implications for the origin of complex biomineral shapes in nature. A multilevel modular organization with small intermodular misorientations combines a simple construction scheme, ruled by crystallographic laws, with the possibility of complex shapes. If the observations we have made on red coral extend to other biominerals, long-range crystallographic order and interfaces at all scales may be key to how some biominerals achieve complex shapes adapted to the environment in which they grow.

The crystal structure and pressure influence (between 0-6 GPa) on 2M 1 muscovite have been calculated by quantum-mechanical methods based on density functional theory (DFT) with optimized numerical LCAO basis sets and norm-conserving pseudopotentials. Tensions between 0.8 and 0 GPa have been also studied. Volumes as a function of pressure, computed from the generalized gradient approximation, are closer to the experimental data than volumes calculated from the local density approximation. The crystal structure, bond distances, and main geometrical features agree with previous experimental values. A third-order Birch-Murnagham equation is fitted, giving a bulk modulus of 60.1 GPa, which reasonably agrees with the experimental data. Axis compressibilities are slightly smaller than those of the experimental data. The most compressible axis is the c axis. Bond strains, angles, the main geometrical features, and polyhedral strains are studied as a function of pressure, and these vary according to the experimental behavior. Tetrahedral <α> and <ρ2> angles and corrugation show an oscillating behavior in the range of pressures used. The most important compressibilities are those related to the interlayer space, as it corresponds to the weakest bonding in the structure. The highest compressibility in the T-O-T layer along the [001] direction is determined by the octahedral sheet thickness. The compressibilities along the a and b axes are determined by the tetrahedra, as the most compressible polyhedra, and the α angle. Therefore, with our results the utility of periodic DFT methods for studying crystal structure and the effect of hydrostatic pressure on 2M 1 muscovite are once again validated, and they are suitable to describe the compression of the crystal structure in detail.

Orthophosphate, (Mg,Fe,Mn) 3 (PO 4 ) 2 with XMg = Mg/(Mg+Fe) = 0-0.89 and Mn/Fe = 0.05-0.3 and chladniite-johnsomervilleite, MnNa 8 (Ca 4 Na 4 )(Mg,Fe,Mn) 43 (PO 4 ) 36 with X Mg = 0.44-0.81 and Mn/Fe = 0.3-0.8, are minor constituents of meteorite Graves Nunataks (GRA) 95209, a transitional acapulcoite consisting mostly of forsterite (Fa7) and enstatite (Wo 3 Fs 7-8 ) with subordinate clinopyroxene (Wo 41-45 Fs 4-6 ) and plagioclase (Or 1-2 An 10-19 ), and cut by Fe,Ni metal veins. Electron backscatter diffraction patterns and maps, together with chemical analyses and Fe-Mg-Mn distribution among phosphates, confirm identification of the orthophosphate as sarcopside, chopinite, and farringtonite; no graftonite was found. Phosphates are found as (1) narrow rims between metal and forsterite or orthopyroxene; (2) aggregates having the same outline as metal; and (3) inclusions and stringers in metal, including a ring around a graphite rosette. Electron microprobe analyses of sarcopside/chopinite-johnsomervilleite/ chladniite pairs give a regular Fe-Mg distribution with KD = (Mg/Fe) Src/Chp /(Mg/Fe) Jhn/Cld = 0.584 consistent with terrestrial sarcopside-johnsomervilleite pairs, whereas analyses of farringtonite-chladniite pairs give K D = 1.51, but the Mg-Fe distribution is less regular. Textural relations suggest that Fe-Mn sarcopside originally formed by oxidation of P in metal and replacement of the metal and, through interaction with silicates, was converted to magnesian sarcopside-chopinite and farringtonite, i.e., the silicate matrix acted as a reservoir of Mg that could be exchanged with Fe and Mn in the sarcopside. Using the farringtonite-chopinite univariant curve determined in hydrothermal experiments by F. Brunet and others, isopleths calculated for the most magnesian chopinite in GRA95209, X Mg = 0.65, give 4-7 kbar at 500-1100 °C, pressures far too high for the acapulcoite-lodranite parent body. Two scenarios could explain the discrepancy: (1) chopinite and magnesian sarcopside persisted metastably into the farringtonite stability field as Mg-Fe exchange progressed and the source volume for GRA95209 cooled; (2) a very mild shock event was intense enough to convert Fe-rich farringtonite (X Fe = 0.4-0.6) to magnesian sarcopside and chopinite, but not enough to deform olivine in the source volume. Whether metastability could have played a role in chopinite formation would best be answered by experiments on the Mg 3 (PO 4 ) 2 -Fe 3 (PO 4 ) 2 system under anhydrous conditions. If the transformation was found to be as kinetically fast as in the hydrothermal experiments, then shock would become the more plausible explanation for the presence of chopinite in this meteorite.

An investigation of rare earth elements (REE) in 15 zircon grains from lunar breccia sample 14321, combined with published analyses, has allowed lunar zircon grains to be separated into four distinctive types. Type-1 zircon is characterized by the relative depletion of light REE (LREE) resulting in a steep chondrite-normalized pattern. Type-2 zircon shows relative enrichment in the LREE compared to type-1 grains. Type-3 zircon also shows relatively high concentrations of LREE as well as a relative depletion in the heavy REE (HREE), which results in a relatively flat chondrite-normalized pattern. Type-4 zircon grains are characterized by the steepest chondrite-normalized REE pattern, with the lowest LREE and the highest HREE as well as by a distinctive positive Ce anomaly. Multiple analyses of REE in a complex impact modified zircon from breccia sample 73235 suggest a possibility that the very light REE from La to Nd were mobilized during impact. However, the main differences between the identified zircon types appear to be primary and reflect the original crystallization environment of zircon grains. These differences are not linked to major changes associated with the different suites of plutonic rocks, such as Mg- and alkali-suites, and quartz monzodiorites (QMD), but instead reflect small-scale variations in residual pockets of melt where zircon grains crystallized. For example, the presence of plagioclase in the immediate vicinity of zircon was responsible for the type-1 zircon REE pattern, whereas type-2 zircon was formed in the presence of pyroxene. The only exception is type-4 zircon, which was probably associated with some felsite and “granite” samples representing very late differentiates of lunar mafic magmas.

Electrical impedance measurements in the laboratory on silicate melts are used to interpret magnetotelluric anomalies. On the basis of 2- and 4-electrode measurements, we show that the influence of the electrodes of the 2-electrode system on the measured resistivity can be of significant importance for low-resistivity melts and increases with temperature. At 1400 °C, the resistivity of very conductive melts measured with two electrodes can reach six times the resistivity value measured with four electrodes. A short-circuit experiment is needed to correct the 2-electrode data. Electrodes contribution is also estimated for samples from other studies, for which the resistance of the electrical cell can be as high as the resistance of the sample. A correction of the resistivity data from the literature is proposed and values of the corresponding Arrhenian parameters are recommended.

There are four ways by which OH- commonly substitutes into olivine, namely those associated with (1) Si vacancies, (2) Mg vacancies, (3) Ti, or (4) trivalent cations. The four mechanisms, which we label [Si], [Mg], [Ti], and [triv], respectively, may each be fingerprinted by their characteristic O-H stretching modes in the infrared spectrum. We show by comparing the integrated intensities of these characteristic infrared peaks against total water content analyzed by secondary ion mass spectrometry, obtained for a suite of synthetic olivines plus one natural olivine, that the different substitution mechanisms require different absorption coefficients (k). For [Ti], we find k = 0.18 ± 0.07, identical to the value previously obtained from natural olivines in which the water was mainly associated with [Ti] defects. Values of k for [Si] and [triv] are 0.57 ± 0.04 and 0.18 ± 0.05, respectively; that for [Mg] is too small to be accurately determined (0.03 ± 0.03). The values of k for [Ti] and [Si] defects differ by a factor of three even though their average wavenumbers are virtually the same. The [Ti] and [triv] defects, on the other hand, have very similar absorption coefficients at significantly different wavenumbers. This highlights the inadequacy of using wavenumber-dependent calibrations for olivine and presumably for NAMs in general. Different substitution mechanisms have their own crystallographic environments that determine their absorption coefficients. The large variation in absorption coefficients within a single mineral emphasizes the importance of distinguishing the substitution mechanism if meaningful quantitative results are to be obtained from infrared spectroscopy.

High-pressure and room-temperature single-crystal X-ray diffraction (XRD) studies have been performed on crystals of a natural pigeonite sample with composition ca. Wo 10 En 43 Fs 47 using diamondanvil cells. The unit-cell parameters were determined at 18 different pressures up to about 6 GPa. A first-order P2 1 /c-C2/c phase transition was found between 3.5 and 3.6 GPa, associated with the disappearance of the b-type reflections (h + k = odd) and a strong discontinuity (about 1.7%) in the unit-cell volume. At the transition, a small hysteresis (~0.3 GPa) was observed. A third-order Birch-Murnaghan equation of state (BM3-EoS) fit to the 10 P-V data of the low-P phase yielded V0 = 431.93(2) Å 3 , KT0 = 96.8(8) GPa and K′ = 8.5(6). A second-order Birch-Murnaghan EoS fit to the 8 P-V data (between 3.6 and 6 GPa) of the C2/c high-P phase yielded V0 = 423.6(1) Å 3 and K T0 = 112.4(8), indicating that the high-P C2/c phase is significantly stiffer than the low-P phase. In a separated experiment with crystals of the same sample, intensity data were collected and crystal structures were refined at 13 pressures up to 9.4 GPa. The M1-O and M2-O mean bond lengths of the low-P P2 1 /c phase decrease by 0.7 and 2.1%, respectively. The two non-equivalent A and B tetrahedral chains become more kinked with pressure, with a reduction of their angle by 2.2 and 5.1%, respectively. At the transition the A-chain changes sense of rotation and both chains become equivalent and more kinked, with a further reduction of their angle by 2.5% up to 9.4 GPa. Strain calculations have been performed and the evolution of the spontaneous strain and the order parameter variation with pressure are discussed, considering geometrical parameters of the structure and comparing our results with the available data for other compositions.

Anhydrous and hydrous wadsleyite were synthesized at 13.3-13.5 GPa and 1150-1200 °C in a multianvil press and investigated by Fourier transform infrared (FTIR) spectroscopy, single-crystal X-ray refinement (SC-XRD), and electron microprobe analyses (EMPA). The FTIR spectra agree with previous data, i.e., the spectra are dominated by a broad band around 3380 cm -1 , resolvable in three bands 3326 (ν 2 ), 3382 (ν 3 ), and 3546 (ν 4 ) cm -1 besides some weaker OH-bands around 3600 cm -1 . We confirm that wadsleyite incorporates water in the wt% range and that the concentration strongly increases with decreasing temperature when using secondary ion mass spectrometry (SIMS) and Raman spectroscopy. The quantifications combined with FTIR spectra led us to develop the first IR calibration for water in wadsleyite, i.e., calculating an ε i,tot of 73 000 ± 7000 (L mol -1 H₂O cm -2 ). A SC-XRD determination of hydrous wadsleyite FD0718, bearing 8000 ± 1000 wt ppm H 2 O, certifies the presence of Mg vacancies at the M3 sites as previously suggested. Furthermore, we found maxima in the electron density map close to the O atoms O1 and O3 of an M3 octahedron assuming the anhydrous structure. Based on our new data we suggest that the main protonation in wadsleyite occurs along the O1···O4 (3.1 Å) and O3···O4 (3.05 Å) edges of a vacant M3 octahedron. H-incorporation seems to be random leading to protonation of either two O1, two O3, or one O1 and one O3 of the vacant M3 octahedra. With this assignment, the observed ambient and high-pressure IR pattern can now be explained.

Polarized spectra of natural brownish-yellow Fe-rich staurolite from Pizzo Forno (Switzerland) evidence that its color is very likely due to an intervalence charge-transfer transition between Fe 2+ and Ti 4+ that causes a broad absorption band at ca. 25 400 cm -1 superimposed on an intense high-energy edge. The polarization properties of the band and, also, the visible pleochroism γ > α >> β of the sample studied, which is found to be different to previously published data viz. γ > β >> α, does not unambiguously give evidence of the structural positions of Ti 4+ ions involved in the IVCT process. In the NIR-range, we observe a broad structured absorption envelope caused by an electronic spinallowed band of IVFe 2+ containing three broad components at around 5445, 4625, and 3800 cm-1 and strong narrow β- and γ-polarized lines of OH-vibrations in the range 3600 to 3400 cm -1 . Curve-fitting analysis suggests that the three crystal field bands are due to lowering of the local symmetry of the tetrahedral Fe 2+ from T d to ca. C 2v , so they are assigned to the split electronic 5 E → 5 T 2 transition of IV Fe 2+ . Noticeable differences in the temperature- and pressure-induced effects on the spin-allowed bands of IV Fe2+ in staurolite compared to spinel-another IV Fe 2+ -bearing mineral-are observed. This implies a suppression of the Jahn-Teller effect in staurolite that is normally intrinsic to ions with doublefold degenerate electronic ground state such as IV Fe 2+ .

Metasideronatrite was obtained as the first dehydration product of sideronatrite, Na 2 Fe(SO 4 ) 2 (OH)∙3H 2 O, from Sierra Gorda, Chile. The crystal structure of metasideronatrite was solved by direct methods and refined by full-matrix least-squares to R = 0.039, using 574 independent reflections with I > 3.0σ(I). It is orthorhombic, space group Pbnm, with a = 7.3959(8), b = 16.0979(15), c = 7.1607(8) Å, V = 852.5(2) Å 3 , Z = 4. The crystal-chemical formula derived from this structural study is Na2Fe(SO 4 ) 2 (OH)∙H 2 O. The backbone of the structure is the same as that in sideronatrite: infinite [Fe 3+ (SO 4 ) 2 (OH)] 2- chains of interconnected octahedra and tetrahedra parallel to the c axis. These chains are linked primarily by Na atoms to build a 3-dimensional network of strong (Fe-O-S) and weak (Na-O) bonds. Another prominent feature of the structure is the arrangement of distorted (NaO 5 H 2 O) octahedra, which alternately share one edge and one face to form columns parallel to the [Fe 3+ (SO 4 ) 2 (OH)] chains. Subsidiary intra-chain bonds are provided by H atoms belonging to OH- groups shared by adjacent Fe octahedra, and to the unique water molecule shared between two adjacent (NaO 5 H 2 O) octahedra. At normal conditions of relative humidity (RH) and temperature (i.e., RH > 60% and T < 40 °C), metasideronatrite rehydrates rapidly to sideronatrite. The structure solution has allowed us to: (1) investigate the strong relation between sideronatrite and metasideronitrite; (2) elucidate the mechanism involved in the transformation of metasideronatrite into the order/disorder (OD) structure of sideronatrite; and (3) get insight into the stability of this mineral from the valence-matching principle applied to the main structural unit [Fe 3+ (SO 4 ) 2 (OH)] 2 and Na + interstitial species. The weak hydrogen bonds and the particular arrangement of the face-sharing adjacent [NaO 5 (H 2 O)] octahedra are the main factors affecting the stability of metasideronatrite.

A spectroscopic study on seven natural zircon crystals representing varying coloration and degree of short-range order has been conducted using Raman, optical absorption (OA), time-resolved laserinduced luminescence (TRL), and electron paramagnetic resonance (EPR) spectroscopy. There is a systematic increase in the line width of the central Gd 3+ transition in the EPR spectra with decreasing short-range order as defined by Raman spectroscopy. In the luminescence spectra, the broad-band yellow photoluminescence centered at about 560 nm is restricted to samples with a high degree of short-range order. In contrast, photoluminescence related to trivalent rare earth elements was detected in zircon with both intermediate and high degrees of short-range order, but not in one heterogeneous, intermediate to highly metamict sample. Furthermore, short-lived greenish luminescence, typical of uranyl ions, could be detected in the luminescence spectra of partly and strongly metamict zircon. Reabsorption lines related to the presence of tetravalent U were found in luminescence spectra of both well-ordered and metamict samples. These observations give evidence for the occurrence of hexavalent U, besides the tetra- and pentavalent forms in natural zircon. It appears that pentavalent U initially present in crystalline zircon converted to tetra- and hexavalent U in highly metamict samples. For a well-ordered green zircon crystal from Caldas Minas, Minas Gerais (Brazil), spectra of Mn 2+ (or Mn 4+ ) were detected by both EPR and luminescence spectroscopy, demonstrating that Mn centers may be present in this mineral. Potential color centers are discussed. Green coloration of natural zircon cannot be assigned exclusively to the presence of U 4+ as suggested previously. Furthermore, no significant influence of the Nb 4+ center on zircon coloration, including reddish color, was found. Yellow coloration may be related to the absorption due to charge-transfer bands of Pr 4+ .

Several finely dispersed low-temperature dioctahedral micas and micaceous minerals that form solid solutions from (Mg,Fe)-free illite to aluminoceladonite via Mg-rich illite, and from Fe 3+ -rich glauconite to celadonite have been studied by X-ray diffraction and chemical analysis. The samples have 1M and 1Md structures. The transitions from illite to aluminoceladonite and from glauconite to celadonite are accompanied by a consistent decrease in the mica structural-unit thickness (2:1 layer + interlayer) or csinβ. In the first sample series csinβ decreases from 10.024 to 9.898 Å, and in the second from 10.002 to 9.961 Å. To reveal the basic factors responsible for these regularities, structural modeling was carried out to deduce atomic coordinates for 1M dioctahedral mica based on the unit-cell parameters and cation composition. For each sample series, the relationships among csinβ, maximum and mean thicknesses of octahedral and tetrahedral sheets and of the 2:1 layer, interlayer distance, and variations of the tetrahedral rotation angle, α, and the degree of basal surface corrugation, ΔZ, have been analyzed in detail. The transitions from illite to aluminoceladonite and from glauconite to celadonite are accompanied by a slight increase in the mean thickness of the 2:1 layers and a steady decrease in the α angles, whereas the interlayer distance becomes smaller. These results are consistent with the generally accepted model where tetrahedral rotation is the main factor for the interlayer contraction in muscovitephengite structures: the smaller the rotation angle (α) the larger the ditrigonal ring of the tetrahedral sheet and the interlayer pseudo-hexagonal cavity, allowing the interlayer cation to sink and thus shorten the c parameter. A new insight into the interpretation of the contraction of the mica layer thickness in dioctahedral micas has been achieved with the discovery that micas with the same or close mean interlayer distance, on one hand, have the same or nearly the same substitution of Al for Si; and on the other hand, they may have significantly different parameters of the interlayer structure, such as tetrahedral rotation, basal surface corrugation, ΔZ, and minimum and maximum interlayer distance. These results show that in dioctahedral 1M micas, the mean interlayer distance is determined by the amount of tetrahedral Al because the higher the Al for Si substitution, the stronger the repulsion between the basal O atoms and the larger the interlayer distance and csinβ parameter.

Diffusion of rare earth elements has been characterized in synthetic forsterite and natural olivine (Fo 90 ) under dry conditions. Experiments were prepared by enclosing source material [mixtures of rare-earth element (La, Dy, or Yb) aluminate and synthetic forsterite powders in 3:1 proportions] and polished forsterite in platinum capsules. For buffered experiments on natural olivine, samples were placed with the source in AgPd capsules, sealed under vacuum in silica glass ampoules with a solid buffer (NNO, IW, or graphite ). In some experiments, ground natural olivine was also incorporated into the source material. Prepared capsules were annealed in 1 atm furnaces for one hour to several weeks at 850 to 1300 °C. REE distributions in olivine were profiled by Rutherford backscattering spectrometry (RBS). The following Arrhenius relation is obtained for Dy diffusion in forsterite: D Dy = 8.0 × 10 -10 exp(-289 ± 21 kJ mol -1 /RT) m 2 /s. Diffusivities of Yb and La in forsterite and for Dy in natural olivine are similar. Experiments run on natural olivine show little dependence of diffusion on crystallographic orientation. The Arrhenius relation yields diffusivities about three orders of magnitude smaller than those determined for REE diffusion in olivine by Spandler et al. (2007) and suggests that timescales for preservation of REE signatures in olivine-hosted melt inclusions may be relatively long. REE diffusivities in olivine are an order of magnitude faster than those of REE +3 in enstatite (Cherniak and Liang 2007) and in diopside under most conditions (Van Orman et al. 2001). Hence, REE signatures in olivine are more likely to be altered by diffusion than those of clinopyroxene or orthopyroxene.

Eleven compositions along the join Na(NaMg)Mg 5 Si 8 O 22 (OH) 2 -Na(NaCa)Mg 5 Si 8 O 22 (OH) 2 (“magnesiorichterite”-richterite) have been synthesized at T = 800-850 °C and P H₂O = 0.35-0.5 GPa. The run products have been characterized by electron probe microanalysis (EPMA), synchrotron and conventional X-ray powder diffraction (XRPD), Fourier transformed infrared (FTIR) spectroscopy, and selected area electron diffraction (SAED-TEM). Nominally, the chemical variation along the join can be expressed as B Mg x B Ca 1-x with 0 ≤ x ≤ 1. A combination of EPMA and FTIR data in the OH-stretching region show that a complete solid solution is obtained under the conditions used. Nevertheless, a slight deviation from the nominal compositions involving a limited loss of Na at A and B sites, balanced by an increase of Ca at the B site, is present. Several indications of a displacive and coelastic P2 1 /m → C2/m transformation induced by the Ca-Mg chemical substitution are observed. The phase transition occurs at B-site composition (X c ) close to B(Na 1 Mg 0.7 Ca 0.3 ). C2/m samples with a Ca content of 0.34, 0.45, and 0.54 apfu show a significant strain tail related to local compositional inhomogeneities. This residual strain disappears as the amount of B Ca significantly increases with respect to that of B Mg. The transformation behavior observed here mirrors that of pyroxenes along the join diopside (CaMgSi 2 O 6 )-enstatite (Mg 2 Si 2 O 6 ). The cell parameters of amphiboles with CMg 5 , TSi 8 , and W(OH) 2 and variable A- and B-site populations follow almost linear and continuous trends, indicative of small amounts of spontaneous strain accompanying these monoclinic phase transitions and the absence of significant miscibility gaps among different amphibole groups when quenched from higher temperatures of crystallization.

Aiolosite, ideally Na 4 Bi(SO 4 ) 3 Cl, or better Na 2 (Na 2 Bi)(SO 4 ) 3 Cl, is a new sulfate mineral isotypic to apatite. It was found in an active medium-temperature intracrater fumarole at La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. It occurs as acicular to slender prismatic crystals up to 0.5 mm long in an altered pyroclastic breccia, together with alunite, anhydrite, demicheleite-(Br), demicheleite-(Cl), bismuthinite, and panichiite. The symmetry is hexagonal (class 6/m), space group P63/m, with a = 9.626(3), c = 6.880(3) Å, V = 552.1(3) Å 3 , Z = 2. The habit is prismatic, terminated by the pinacoid or, more rarely, by a bipyramid. Aiolosite is colorless to white, with white streak; the luster vitreous. It is non-fluorescent. The calculated density is 3.589 g/cm 3 . The mineral is nonpleochroic, uniaxial (+), n ω = 1.59(1), n ε = 1.60(1), mean n obs = 1.593 (589 nm), n calc = 1.620. The chemical analysis gave Na 2 O 20.65, K 2 O 0.96, Bi 2 O 3 32.49, SO 3 41.27, Cl 4.02, Br 0.75, (H 2 O 0.57 from structure refinement), -O = (Cl + Br) 0.98 wt%, total 99.73, corresponding to the empirical formula calculated on the basis of 13 anions: Na 2 (Na 1.95 K 0.12 Bi 3+ 0.83 ) Σ2.90 S 3.06 O 12.08 [Cl 0.67 Br 0.06 (H 2 O) 0.19 ] Σ0.92 . The crystal structure has been refined to a final R index of 0.048. One of the two independent Ca sites of apatite is exclusively occupied by Na, and the other one by statistically distributed Na and Bi. The SO 4 2- anion replaces the PO 4 3- anion of apatite; the chloride anion is located in the partially occupied (s.o.f. = 0.81) position at x = 0, y = 0, z = 0. Whenever the chloride position is vacant, the position at x = 0, y = 0, z = 1/4 is occupied by water (s.o.f. = 0.19). The strongest 6 lines in the X-ray powder diffraction pattern [d obs (Å) (I) hkl] are: 2.853 (100) (121), 2.775 (85) (112), 3.432 (45) (002), 1.965 (35) (222), 2.306 (25) (310), 4.787 (20) (110). Both the mineral and the mineral name have been approved by the IMA CNMNC (No. 2008-015).

Gayite, ideally NaMn 2+ Fe 3+ 5 (PO 4 ) 4 (OH) 6 ·2H 2 O, is a new member of the dufrénite group found at the Gigante granitic pegmatite, Punilla department, Córdoba province, Argentina. It is named for Hebe D. Gay (b. 1927), Professor Emeritus of Mineralogy of the National University of Córdoba (Argentina). The new mineral is monoclinic, space group C2/c, a = 25.975(3) Å, b = 5.1766(3) Å, c = 13.929(1) Å, β = 111.293(2)°, Z = 4. The strongest lines in the X-ray powder diffraction pattern are [d in Å, (I)]: 12.054 (33), 5.045 (60), 4.147 (37), 3.424 (71), 3.179 (100), 3.004 (33), 2.881 (42), 2.426 (36), 2.109 (39), 1.585 (50). It occurs associated with morinite, natrodufrénite, and quartz in cavities in massive apatite-(CaF), as clusters of tabular crystals up to 130 μm on edge dominated by {100}, with subordinate {201̄} and possibly also {110}, {111}, and {111̄}. Crystals display striations parallel to [010]. The mineral is greenish black with an olive green streak and vitreous luster. Thin tablets are transparent. Gayite is brittle, with perfect {100} cleavage and irregular fracture. Its Mohs hardness is 4 to 5. The measured density is 3.15(5) g/cm 3 , and the calculated density is 3.241 g/cm 3 . The mineral dissolves slowly in dilute HCl. Gayite is biaxial (+), α = 1.787(3), β = 1.792(3), γ = 1.806(3), 2V meas = 60(5)°, 2V calc = 62.1°; moderate dispersion, r < v; strong pleochroism, X (bluishgreen) >> Z (orange) > Y (yellow); orientation Y = b, X ^ a = 48° in obtuse β. Analysis by electron microprobe (average of 28 analyses given in wt%) provided TiO 2 0.12, Al 2 O 3 3.10, Fe 2 O 3 41.95, MnO 5.97, MgO 0.08, CaO 0.23, ZnO 0.15, Na 2 O 3.03, P 2 O 5 32.73, and H 2 O (calculated by stoichiometry) 10.31, total 97.67 wt%. The empirical formula, based on 24 O, is (Na 0.85 Ca 0..02 ) Σ0.87 (Mn 2+ 0.74 Fe 2+ 0.12 Mg 0.02 Zn 0.02 Ti 4+ 0.01 ) Σ0.90 (Fe 3+ 4.47 Al 0.53 ) Σ5.00 (P 4.03 O 16 )(OH) 6 ·2H 2 O. The crystal structure (R1 = 6.10%) shows gayite to be a member of the dufrénite group, along with dufrénite, natrodufrénite, matioliite, and burangaite. The structure is a framework consisting of Fe 3+ O 6 octahedra, Mn 2+ O 6 octahedra, and PO 4 tetrahedra with channels along the b axis containing Na atoms. The most unusual feature of the structure is an octahedral face-sharing Fe 3+ -Mn 2+ -Fe 3+ trimer.

Galliskiite, ideally Ca 4 Al 2 (PO 4 ) 2 F 8 ·5H 2 O, is a new mineral found at the Gigante granitic pegmatite, Punilla department, Córdoba Province, Argentina. It is named for Argentine mineralogist and pegmatite specialist Miguel Ángel Galliski. Galliskiite is triclinic, P1̄, a = 6.1933(7), b = 9.871(1), c = 13.580(2) Å, α = 89.716(3), β = 75.303(4), γ = 88.683(4)°, Z = 2. The strongest lines in the X-ray powder diffraction pattern are [d in Å, (I)]: 7.904 (70), 5.994 (100), 3.280 (58), 3.113 (30), 2.945 (85), 2.887 (44), 2.483 (20), 2.262 (27), 2.150 (23), 1.821 (27), and 1.798 (25). It occurs as crude platy crystals elongated along [001] and flattened on {010}, with frosty surfaces. Simple contact and polysynthetic twinning on {100} by rotation about [010] is ubiquitous. It is colorless and transparent, has white streak and vitreous luster, and is nonfluorescent under ultraviolet radiation. It has a Mohs hardness of 2½, conchoidal to irregular fracture and two fair cleavages at approximately 90°. The measured density is 2.67(3) g/cm 3 , and the calculated density is 2.670 g/cm 3 . Galliskiite dissolves slowly in concentrated HCl. The mineral is biaxial (+), α = 1.493(1), β = 1.495(1), γ = 1.520(1), 2V meas = 33(5)°, 2V calc = 32°; dispersion, r < v; orientation Z ≈ b, X and Z at 40-50° from a and c. No pleochroism is observed. Analysis by electron microprobe (average of 12 analyses given in wt%) provided CaO 34.71, MgO 0.01, FeO 0.10, MnO 0.17, Al 2 O 3 15.92, SiO 2 0.06, TiO 2 0.01, P 2 O 5 21.94, F 21.35, H 2 O (calculated by stoichiometry) 15.08, less F≡O 8.99, total 100.39 wt%. The empirical formula, based on 21 (F+O), is (Ca 3.98 Mn 0.02 Fe 0.01 ) Σ4.0 Al 2.01 (P 1.99 Si 0.01 O 8 )F 7.23 (OH) 0.77 ·5H 2 O. The crystal structure, solved and refined using single-crystal data to R 1 = 0.033, consists of double chains of alternating corner-sharing AlF 3 O 3 octahedra and PO 4 tetrahedra along the a axis. The chains are joined into a framework via bonds to four distinct Ca atoms. Calcium atoms are also linked by sharing isolated F atoms and H 2 O molecules. The double-chain motif in the structure of galliskiite is distinct from that in any other known phosphate.

Liversidgeite, ideally Zn 6 (PO 4 ) 4 ·7H 2 O, is a new mineral from Block 14 Opencut, Broken Hill, New South Wales, Australia. The mineral occurs as white, thin, bladed crystals and as hemispherical aggregates of radiating crystals in cavities in sphalerite-galena ore. Associated minerals are anglesite, pyromorphite, greenockite, sulfur, and an unknown Zn phosphate sulfate. Individual crystals are up to 0.1 mm in length and 0.05 mm across. Liversidgeite is transparent to translucent, with a vitreous luster and a white streak. It is brittle with an irregular fracture, the Mohs hardness is ~3-3.5, and the observed and calculated densities are 3.21(2) and 3.28 g/cm 3 , respectively. Chemical analysis by electron microprobe gave ZnO 54.62, MnO 0.49, PbO 0.18, P 2 O 5 32.62, As 2 O 5 0.65, SO 3 0.35, H 2 O 14.04, total 102.95 wt%, with H 2 O content derived from the refined crystal structure. The empirical formula calculated on the basis of 23 O atoms is Pb 0.01 (Zn 5.86 Mn 0.06 ) Σ5.92 (P 4.01 As 0.05 S 0.04 ) Σ4.10 O 16.20 ·6.8H 2 O. Liversidgeite is triclinic, space group P1̄, with a = 8.299(1), b = 9.616(1), c = 12.175(1) Å, α = 71.68(1), β = 82.02(1), γ = 80.18(1)°, V = 905.1(2) Å 3 (single-crystal data), and Z = 2. The six strongest lines in the X-ray powder diffraction pattern are [d(Å), (I), (hkl)]: 8.438 (80) (011), 3.206 (60) (013̄), 2.967 (75) (21̄2, 114), 2.956 (75) (212̄), 2.550 (85) (233, 21̄3), 2.537 (100) (221̄, 014̄, 311̄). The crystal structure of liversidgeite was refined to an R1 index of 5.95% based on 3054 observed (Fo > 4σFo) reflections measured with MoKα X-radiation. The structure is based on two distinct, infinite zigzag chains of edge-sharing Znφ 6 (φ = unspecified anion) octahedra that extend in the a direction. The chains link to each other via common corners and also via corner-sharing PO 4 tetrahedra, forming sheets parallel to the (011) plane. The sheets link via [Zn 2 φ 8 ] dimeric building units, comprising edge-sharing Znφ 5 trigonal bipyramids and Znφ 4 tetrahedra, resulting in an open framework. Large ellipsoidal channels extend along the a direction and are occupied by interstitial H 2 O groups and the H atoms of the H 2 O groups that coordinate to the Zn cations. An extensive network of hydrogen bonds provides additional linkage between the sheets in the structure, via the interstitial H 2 O groups. The topology of the liversidgeite structure is identical to that of synthetic, monoclinic Zn 2 Co 4 (PO 4 ) 4 (H 2 O) 5 ·2H 2 O.

The determination of the maximum temperature achieved by friction melt (T melt ) in pseudotachylytebearing faults is crucial to estimate earthquake source parameters (e.g., earthquake energy budgets, coseismic fault strength) on a geological basis. Here we investigated the mineralogy of a pseudotachylyte from the Gole Larghe Fault (Italian Alps) by using X-ray powder diffraction, micro-Raman spectroscopy, and EDS-equipped field emission scanning electron microscopy. In particular, we report the presence of the hexagonal polymorph of CaAl 2 Si 2 O 8 (dmisteinbergite) in a pseudotachylyte. Published experimental work shows dmisteinbergite can crystallize at 1200-1400 °C by rapid quenching. Therefore, the presence of dmisteinbergite in pseudotachylyte could be a reliable geothermometer for friction melts for which T melt has only as yet been estimated.

We have determined D Eu between augite and melt in samples that crystallized from a highly spiked martian basalt composition at four f O₂ conditions. D Eu augite/melt shows a steady increase with f O₂ from 0.086 at IW -1 to 0.274 at IW+3.5. This increase is because Eu3+ is more compatible than Eu 2+ in the pyroxene structure; thus increasing f O₂ leads to greater Eu 3+ /Eu 2+ in the melt and more Eu (total) can partition into the crystallizing pyroxene. This interpretation is supported by direct determinations of Eu valence state by XANES, which show a steady increase of Eu 3+ /Eu 2+ with increasing f O₂ in both pyroxene (0.38 to 14.6) and glass (0.20 to 12.6) in the samples. Also, pyroxene Eu 3+ /Eu 2+ is higher than that of adjacent glass in all the samples, which verifies that Eu 3+ is more compatible than Eu 2+ in the pyroxene structure. Combining partitioning data with XANES data allows for the calculation of specific valence state D-values for augite/melt where D Eu3+ = 0.28 and D Eu2+ = 0.07.

We present density functional calculations of vibrational frequencies of OH groups on an idealized goethite (110) surface, represented by a large embedded cluster model. The calculations show that isolated surface groups bound to one, two, and three metal ions can have nearly identical OH stretching frequencies. This finding provides a strong constraint on interpretations of infrared spectra of oxide surfaces, and resolves a long-standing problem in OH vibrational assignments on goethite surfaces, where, in general, too few peaks have been observed relative to the expected heterogeneity of surface functional groups.

The effect of ferric iron on the properties of Mg-silicate post-perovskite (PPv) were studied up to 138 GPa using synchrotron X-ray diffraction and Mössbauer spectroscopy. Our diffraction measurements revealed that the incorporation of Fe 3+ has virtually no effect on the volume of PPv, in contrast to Fe 2+ , which increases the volume. Therefore, incorporation of Fe 3+ increases the density of PPv much more effectively than Fe 2+ . Mössbauer spectroscopy suggests that Fe 3+ enters PPv through chargecoupled substitution and is high spin in the bipolar prismatic site and low spin in the octahedral site (i.e., mixed spin state). Our results may have important implications for the gravitational stability of lower-mantle heterogeneities.