Volume 99, Issue 10

The electron density distribution in a mineral is measureable, and in some ways, provides all the information required to understand the properties of minerals. Through the analysis of the electron density distributions of a large variety of mineral species, Gibbs et al. (2014) examine and challenge the fundamental tenet of Pauling’s Rules, which is that atoms are spheres of a single fixed size. Their analysis provides an updated model of crystal chemistry that is both self-consistent and does what new models should do, explains the older ones.

Vermiculite is a layered silicate with a complex crystalline structure, as it is characterized by the existence of a large density of defects- even in the case of the most pure vermiculite [e.g., Santa Olalla, Huelva (Spain)]. As a result of their lamellar structure, vermiculite structures present a broad diversity of behavior and are interesting from both the applied and scientific point of view. Vermiculite is used to examine interesting physical properties such as mixed-cation effects and two dimensional magnetism. The existence of frustration and disorder is a key feature for understanding the mechanisms of spin-glass, for example. The dimensionality of magnetic interactions, which plays a central role in controlling the critical dynamics of SG systems, is still not resolved. Probably, magnetic studies on structurally ordered vermiculites will elucidate the true nature of spin-glass-like phases. One way to provide structurally ordered vermiculites might be by irradiation with ultraviolet or γ rays. These types of radiation induce structural order in vermiculites leading to materials with enhanced opto-electrical properties, which improve its utility as an electronic insulator and a thermoluminescence dosimeter for innovative dosimetry applications in a radiation-rich environment (Kaur et al. 2014, this issue). Other layered minerals irradiated with γ rays exhibit enhanced radiation shielding capacities and electronic insulating properties.

As metamorphic petrologists attempt to understand the pressure-temperature-time-deformational history of metamorphic rocks, numerous thermobarometers have been developed that help recreate that history. As these thermobarometers are developed, they invariably mature as they are tested on various metamorphic assemblages. In the work “Ti resetting in quartz during dynamic recrystallization: Mechanisms and significance,” by Ashley et al. in this issue, the authors demonstrate that the metamorphic process of dynamic recrystallization of quartz lowers the [Ti] in quartz as recrystallizing quartz crystals re-equilibrate in equilibrium with the composition of the intergranular medium, which is typically undersaturated in Ti. The authors conclude that analyses using the TitaniQ thermobarometer in rocks that contain dynamically recrystallized quartz cannot be meaningfully interpreted until methods are developed that can account quantitatively for the reduction of [Ti] resulting from crystal plastic flow. The paper is essential reading for all who use thermobarometers that use quartz as one of the reacting phases.

Remote sensing observations have identified aluminate spinel, in the absence of measureable olivine and pyroxene, as a globally distributed component of the lunar crust. Earlier remote sensing observations and returned samples did not indicate the presence of this component, leaving its geologic significance unclear. Here, we report visible to mid-infrared (V-IR) reflectance (300-25 000 nm) and Mössbauer spectra of aluminate spinels, synthesized at lunar-like oxygen fugacity (ƒ O2 ), that vary systematically in Fe abundance. Reflectance spectra of particulate (<45 mm), nominally stoichiometric aluminate spinels display systematic behavior, with bands at 700, 1000, 2000, and 2800 nm increasing in strength with increasing bulk Fe content. The especially strong bands at 2000 and 2800 are discernible for all spinel compositions and saturate at <15 Fe# [Fe/(Mg+Fe)×100, molar]. Absorption bands at 700 and 1000 nm, collectively referred to as the 1000 nm bands, are weaker and become observable at >6 Fe#. Although the 2000 and 2800 nm bands are assigned to Fe 2+ IV electronic transitions, spectra of aluminate spinels with excess Al 2 O 3 demonstrate that the strengths of the 1000 nm bands are related to the abundance of Fe 2+ VI . The abundance of Fe 2+ VI depends on bulk Fe content as well as factors that control the degree of structural order-disorder, such as cooling rate. Consequently the strength of the 1000 nm bands are useful for constraining the Fe content and cooling rate of remotely sensed spinel. Controlling for cooling rate, particle size, and ƒ O2 , we conclude that spinels with >12 Fe# (<88 Mg#) have observable 1000 nm bands under ambient lunar conditions and that only very Mg-rich spinels lack 1000 nm bands in their spectra. This links remote observations of spinel anorthosite to Mg-Suite magmatism. The combined effects of Fe oxidation state, abundance of coexisting plagioclase, and space weathering have not been explored here, and may add additional constraints. The relative strengths of the distinctive 1000 and 2000 nm bands of the spinels associated with pyroclastic deposits at Sinus Aestuum suggest fast cooling rates, possibly in the absence of an extensive vapor cloud.

Lunar highlands are plagioclase-rich terrains produced by crystal floating in a Magma Ocean system. Lunar samples revealed the presence of anorthositic (plagioclase > 90%) samples from the Highlands, associated to more mafic rocks. Recently, remote sensing data permit mapping those terrains with high spatial and spectral resolution allowing detection of plagioclase and mafic crystal field (C.F.) absorptions. In this paper we have studied bidirectional spectral characteristics in the visible near-infrared (VNIR) of rocks from the Stillwater Complex, a cumulitic igneous stratified complex, with composition varying from mafic to sialic (e.g., pyroxenite, anorthosite). We investigated both slabs and powders of these rocks to give indication of the spectral variability of rock analogs of lunar crust, from a mineralogical point of view. Samples have been spectrally separated in four main groups considering the different C.F. absorption association, reflectance and spectral shape for both slab and powder spectra. More spectral details can be obtained from the analysis of powder spectra than from the slab spectra. The composition of rocks can be addressed by studying spectral parameters, such as the position and the intensity of the absorption (e.g., band center and band depth). The analysis of our plagioclasepyroxene- bearing samples indicates that mafic composition can be clearly obtained for samples characterized by one pyroxene phase, even for few amounts of pyroxene, from powder spectra. On the other hand, slab spectra show clear pyroxene absorptions only for rocks with mafic abundance at least >20%. The intensity of the mafic absorptions of these samples shows a linear trend with respect to the abundance of pyroxenes (orthopyroxene + clinopyroxene, for samples with ferrosilite amount less than ca. 25%). Considering all pyroxene-bearing samples, the band depth of slab spectra are linearly related to the volumetric distribution of ferrous iron in pyroxenes.

Mg-Al spinel is rare in lunar rocks (Apollo and meteorite collections), and occurs mostly in troctolites and troctolitic cataclastites. Recently, a new lunar lithology, rich in spinel and plagioclase, and lacking abundant olivine and pyroxene, was recognized in visible to near-infrared (VNIR) reflectance spectra by the Moon Mineralogy Mapper (M 3 ) instrument on the Chandrayaan-1 spacecraft at the Moscoviense basin. These outcrop-scale areas are inferred to contain 20-30% Mg-Al spinel. Possible explanations for the petrogenesis of spinel-bearing and spinel-rich lithology(s) range from low-pressure near-surface crystallization to a deep-seated origin in the lower lunar crust or upper mantle. Here, we describe 1-bar crystallization experiments conducted on rock compositions rich in olivine and plagioclase that crystallize spinel. This would be equivalent to impact-melting, which is moderately common among lunar plutonic rocks and granulites. To explore possible precursor materials and the maximum amount of spinel that could be crystallized, a lunar troctolitic composition similar to Apollo pink spinel troctolite 65785, and a composition similar to ALHA81005 as analog to the source region of this meteorite have been chosen. The crystallization experiments on the composition of AHLA 81005 did not yield any spinel; experiments on the composition similar to Apollo 65785 crystallized a maximum of ~8 wt% spinel, much less than the suggested 20-30% spinel of the new lithology detected by M 3 . However, our VNIR spectral reflectance analyses of the experimental run products indicate that the spinel composition of the experimental run products not only appears to be similar to the composition of the spinel lithology detected by M 3 (characteristics of the spinel absorption), but also that the modal abundances of coexisting phases (e.g., mafic glass) influence the spectral reflectance properties. Thus, the spinel-rich deposits detected by M 3 might not be as spinel-rich as previously thought and could contain as little as 4-5 wt% spinel. However, the effect of space weathering on spinel is unknown and could significantly weaken its 2 μm absorptions. If this occurs, weathered lunar rocks could contain more spinel than a comparison with our unweathered experimental charges would suggest.

In the last decade, it has been recognized that the Moon contains significant proportions of volatile elements (H, F, Cl), and that they are transported through the lunar crust and across its surface. Here, we document a significant segment of that volatile cycle in lunar granulite breccia 79215: impactinduced remobilization of volatiles, and vapor-phase transport with extreme elemental fractionation. 79215 contains ∼1% volume of fluorapatite, Ca 5 (PO 4 ) 3 (F,Cl,OH), in crystals to 1 mm long, which is reflected in its analyzed abundances of F, Cl, and P. The apatite has a molar F/Cl ratio of ∼10, and contains only 25 ppm OH and low abundances of the rare earth elements (REE). The chlorine in the apatite is isotopically heavy, at δ 37 Cl = +32.7 ± 1.6‰. Hydrogen in the apatite is heavy at δD = +1060 ± 180‰; much of that D came from spallogenic nuclear reactions, and the original δD was lower, between +350‰ and +700‰. Unlike other P-rich lunar rocks (e.g., 65015), 79215 lacks abundant K and REE, and other igneous incompatible elements characteristic of the lunar KREEP component. Here, we show that the P and halogens in 79215 were added to an otherwise “normal” granulite by vapor-phase metasomatism, similar to rock alteration by fumarolic exhalations as observed on Earth. The ultimate source of the P and halogens was most likely KREEP, it being the richest reservoir of P on the Moon, and 79215 having H and Cl isotopic compositions consistent with KREEP. A KREEP-rich rock was heated and devolatilized by an impact event. This vapor was fractionated by interaction with solid phases, including merrillite (a volatile-free phosphate mineral), a Fe-Ti oxide, and a Zr-bearing phase. These solids removed REE, Th, Zr, Hf, etc., from the vapor, and allowed the vapor to transport primarily P, F, and Cl, with lesser proportions of Ba and U into 79215. Vapor-deposited crystals of apatite (to 30 μm) are known in some lunar regolith samples, but lunar vapor has not (before this) been implicated in significant mass transfer. It seems unlikely, however, that phosphate-halogen metasomatism is related to the high-Th/Sm abundance ratios of this and other lunar magnesian granulites. The metasomatism of 79215 emphasizes the importance of impact heating in the lunar volatile cycle, both in mobilizing volatile components into vapor and in generating strong elemental fractionations.

Anorthositic rocks dominate the Moon’s upper crust. As remnants of the lunar magma ocean (LMO), small variations in the mineralogy of these rocks may hold key information about the homogeneity of LMO composition and solidification processes. Orbital near-infrared (NIR) sensors are sensitive to mineralogy, but technologic advances have only recently enabled detection of the plagioclase component in crustal rocks based on an absorption band centered near 1250 nm. Anorthosites occupy a unique mineralogic range that is well suited for NIR studies: the highly transparent component, plagioclase, is present in high abundances while the spectrally dominant mafic or oxide minerals are present in only minor abundance. As a result, spectra of anorthosites are more likely than many other rock types to contain visually discernable signatures from more than one mineral component, facilitating their identification and characterization in NIR data. In support of new NIR measurements for the Moon, we present laboratory spectral analyses of well-controlled plagioclase-dominated mineral mixtures. We focus on the spectral effects of varying mafic and oxide composition and abundance in mixtures with a common plagioclase end-member. The results demonstrate that plagioclase can be a significant contributor to reflectance spectra when strongly absorbing minerals are present in low abundance. We show that the contribution of plagioclase is more pronounced in mixtures with pyroxenes and certain spinels, but more easily masked in mixtures containing small amounts of olivine. Differences in minor mineral composition are clearly expressed in bulk spectra. Modeling of mixtures using a Hapke nonlinear approach accurately estimates mineral abundances in laboratory spectra to within 5 vol% for mixtures with ≥90 vol% plagioclase. Together, these results imply that not only should orbital NIR data sets be able to discern the presence of plagioclase in anorthositic crustal exposures, but also that detailed information about anorthosite mineral assemblages can be reliably accessed in reflectance spectra.

A robust assessment is made of the distribution and (spatially resolved) geologic context for the newly identified rock type on the Moon, a Mg-spinel-bearing anorthosite (pink-spinel anorthosite, PSA). Essential criteria for confirmed detection of Mg-spinel using spectroscopic techniques are presented and these criteria are applied to recent data from the Moon Mineralogy Mapper. Altogether, 23 regions containing confirmed exposures of the new Mg-spinel rock type are identified. All exposures are in highly feldspathic terrain and are small-a few hundred meters-but distinct and verifiable, most resulting from multiple measurements. Each confirmed detection is classified according to geologic context along with other lithologies identified in the same locale. Confirmed locations include areas along the inner rings of four mascon basins, knobs within central peaks of a few craters, and dispersed exposures within the terraced walls of several large craters. Unexpected detections of Mg-spinel are also found at a few areas of hypothesized non-mare volcanism. The small Mg-spinel exposures are shown to be global in distribution, but generally associated with areas of thin crust. Confirmation of Mg-spinel exposures as part of the inner ring of four mascon basins indicates this PSA rock type is principally of lower crust origin and predates the basin-forming era.

Chevkinite-(Ce) and perrierite-(Ce) are the most common members of the chevkinite group of minerals. They are dimorphs, and both have the general formula A 4 BC 2 D 2 Si 4 O 22 , where A = REE, Y, Ca, Sr, Th; B = Fe 2+ , (Mn, Mg); C = Ti, Al, Fe 3+ , Fe 2+ , Cr, Mn, Mg, Zr, Hf, Nb; and D = Ti. Both have been reported from a wide range of igneous, metamorphic, and hydrothermal rocks types, but occurrences in mafic rocks are rare, with minimal chemical and crystallographic documentation. Chevkinite-(Ce) and/or perrierite-(Ce) occur with other Ti-, Zr-, and REE-bearing accessory phases in eight suites of tholeiitic dolerite from Western Australia, and in lunar mare basalt 10047. They are more abundant than has been recognized previously in mafic igneous rocks, and they are significant hosts of incompatible elements. Chevkinite-(Ce) and perrierite-(Ce) from mafic rocks have distinctive chemical compositions with higher Zr than recorded in examples from most other common rock types. Among mafic rocks, two groups are recognized based on total Fe contents in electron microprobe analyses: crystal structural analysis by electron diffraction indicates that the high-Fe group (>8 wt% FeO) is chevkinite-(Ce), while the low-Fe group (<8 wt% FeO) is consistent with perrierite-(Ce), and both minerals can occur within a single hand specimen. A previously proposed chemical discriminant is not applicable to chevkinite-group minerals from typical mafic igneous rocks and crystal structural information is required to unequivocally distinguish between the two dimorphs.

Garnet and other rock-forming minerals from A-type granite dikes in the Pre-Variscan Brno Batholith were analyzed to determine relative contributions of individual minerals to whole-rock Y and REE budget and to assess incorporation mechanisms of these elements in garnet. Minor to accessory garnet (<2 vol%) is the essential reservoir for Y+REE in the Hlína granite accounting ∼84% Y and 61% REE of the total whole-rock budget. Zircon is another important carrier of REE with ∼13% Y and ∼11% REE. At least ∼21% REE and 1% Y were probably hosted by Th- and U-rich monazite that has been completely altered to a mixture of secondary REE-bearing phases. The contribution of major rockforming minerals (quartz and feldspars) is low (∼1% Y; 10% LREE; ∼1% HREE) excluding Eu, which is hosted predominantly by feldspars (∼90%). Minor to accessory muscovite and magnetite incorporate ∼1% Y and ∼2% REE of the whole-rock budget. Magmatic garnet Sps 41-46 Alm 28-44 And 0-13 Grs 6-12 Prp 0-1 is Y- and HREE-rich (up 1.54 wt% Y; up ∼1 wt% ΣREE), and the Y+REE enter the garnet structure via the menzerite-(Y) substitution. The Y and REE show complex zoning patterns and represent sensitive indicator of garnet evolution, in contrast to a homogeneous distribution of major divalent cations. General outward decrease of Y+REE is a common feature due to the strong partitioning of Y+HREE in the garnet relative to the other phases. REE underwent significant fractionation during growth of early garnet I; the YbN/NdN ratio generally decreases from the core to rim of garnet I. Higher Mn and Al, lower Ca, and Y+REE contents, as well as higher Yb N /Nd N ratio and more negative Eu anomaly in garnet II overgrowths indicate its crystallization from a more evolved melt. Application of zircon saturation geothermometry provides upper temperature limit of 734 ± 14 °C for the closed-system crystallization. Mineral equilibria reveal that crystallization started at QFM + 1.2, and preferential sequestration of Fe3+ into garnet and magnetite was responsible for progressively reducing conditions. Equilibrium between magnetite, garnet, quartz, and plagioclase, representing the final crystallization stage of the granitic magma, occurred at 658-663 °C and QFM 0 to + 0.8, hence at undercooling of ∼75 °C.

We have determined the mid-IR optical constants of one alkali feldspar and four pyroxene compositions in the range of 250-4000 cm -1 . Measured reflectance spectra of oriented single crystals were iteratively fit to modeled spectra derived from classical dispersion analysis. We present the real and imaginary indices of refraction (n and k) along with the oscillator parameters with which they were modeled. While materials of orthorhombic symmetry and higher are well covered by the current literature, optical constants have been derived for only a handful of geologically relevant monoclinic materials, including gypsum and orthoclase. Two input parameters that go into radiative transfer models, the scattering phase function and the single scattering albedo, are functions of a material’s optical constants. Pyroxene is a common rock-forming mineral group in terrestrial bodies as well as meteorites and is also detected in cosmic dust. Hence, having a set of pyroxene optical constants will provide additional details about the composition of Solar System bodies and circumstellar materials. We follow the method of Mayerhöfer et al. (2010), which is based on the Berreman 4 × 4 matrix formulation. This approach provides a consistent way to calculate the reflectance coefficients in lowsymmetry cases. Additionally, while many models assume normal incidence to simplify the dispersion relations, this more general model applies to reflectance spectra collected at non-normal incidence.

Time-resolved synchrotron X‑ray powder diffraction data were used to investigate the dehydration behavior of the chalcophanite (ZnMn 3 O 7 ·3H 2 O) structure from 300 to 1060 K. Rietveld refinements revealed two obvious phase changes, at ∼450 and ∼950 K, corresponding to the dehydration of chalcophanite followed by transformation to a spinel structure (Mn-hetaerolite). Only small changes were observed in the chalcophanite unit cell from RT to ∼438 K; the volume increased by ∼0.8%, mostly caused by thermal expansion of ∼0.5% along c. Above ∼427 K, the interlayer water molecules were lost, resulting in a collapse of the interlayer spacing from ∼7 to ∼4.8 Å. The newly formed anhydrous phase (ZnMn 3 O 7 ) retained chalcophanite’s R3̅ space group and a dimension, but the c dimension decreased from ∼21 to 14.3 Å, and the Zn coordination changed from octahedral to tetrahedral. Above ∼775 K the anhydrous chalcophanite began to transform to a spinel structure, corresponding to a Mnrich hetaerolite [(Zn 0.75 Mn 2+ 0.25 )Mn 2 3+ O 4 ]. By ∼973 K the transformation was complete. The diffraction patterns did not show a significant increase in background during the transformation, indicating that the reaction did not involve transient amorphization. The phase change was likely triggered by loss of 1.25 of seven O atoms in the original anhydrous chalcophanite structure with a corresponding reduction of Mn 4+ to Mn 3+ and Mn 2+ .

The focus of the study presented here is the illite component of the clay mineral components found within gas shale, specifically the creation of robust, atomistic models of illite particles bearing characteristics of the 2M 1 polytype. The template for the illite models is derived from crystallographic data, which is used together with the general formula, K 1.67 (Al 3.29 Fe 0.38 Mg 0.32 )[(Si 6.68 Al 1.32 )O 20 (OH) 4 ] to create different particles of illite, each containing potassium plus either ammonium (NH 4 + ) or hydronium (H 3 O + ) ions, or water molecules in two different proportions. These atomistic models are optimized from first principles using plane waves and pseudo-potentials within the formalism of density functional theory (DFT). The resulting lattice lengths, lattice dynamics in the form of infrared frequencies, positions of interlayer molecules and simulated X‑ray powder diffraction (XRPD) patterns are analyzed with reference to the available experimental data. We conclude that all four illite models display properties that fall within the range of available experimental data, and that therefore these are state-of-the-art atomistic illites, ready for use in further studies. Furthermore, the analytical data from these models will enable the characterization of physical samples of illite with varying interlayer constituents.

Single-crystal X‑ray diffraction of trona, Na 3 CO 3 HCO 3 ·2H 2 O, was measured between 100 and 340 K at ambient pressures, and the infrared and Raman spectra of this material characterized to ∼25 GPa. The thermal expansion of trona is greatest in the b direction, which is due to a particularly large expansion of the long Na 2 -O 1 and the short Na 2 -O 4 bonds within the sodium septahedron in the trona structure. This crystallographic direction is associated with the distance between neighboring carbonate groups and neighboring water molecules within the structure. The dimensions of the carbonate group undergo no systematic changes over this temperature range, and the disordered hydrogen atom within the structure does not order at temperatures down to 100 K. Thus, detailed changes in the geometry of the sodium polyhedra primarily modulate the response of trona to decreases in temperature. The infrared and Raman spectra undergo discontinuous and reversible changes at ∼7 and ∼14.5 GPa: the former of these phase transitions is likely associated with a shift primarily in the sodium-oxygen polyhedra, while the latter also involves shifts in bonding of the carbonate groups. New assignments are suggested for portions of the vibrational spectrum based on the high-pressure results. Resonance effects between different vibrational modes are observed, including the observation of a transmission maximum associated with a resonant interaction between the carbonate symmetric stretching vibration and a broad mode at similar frequencies. The behavior of trona under extreme conditions is useful for understanding CO 2 -vapor-saturated alkali-rich systems, and late-stage peralkaline magmatic processes and, in its usage as both a sorbent and scrubber of SO 2 and CO 2 in flue gasses and lignite coals.

A laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) study of seven thorite and uranothorite [(Th,U)SiO 4 ] samples ranging in age from ∼13 to ∼500 Ma provides new insights into the U-Th/Pb isotope systematics of these geologically significant, high-Th mineral species. Despite extreme actinide enrichment and complex intra-crystal zonation in actinides and rare earth elements, this study demonstrates that radiogenic-lead loss and/or metamictization is minimal and restricted to domains that have undergone significant hydration. Dating of four igneous uranothorites yields ages that are concordant in U/Pb and Th/Pb space, consistent with other high-temperature chronometers, and are inferred to accurately reflect the timing of crystallization of each rock. Similarly, Th/Pb ages of three thorite and/or huttonite-bearing samples yield geologically plausible dates consistent with other mineral chronometers. No evidence of isotopic inheritance was observed in any of the samples. Data presented here demonstrate for the first time the feasibility of extracting accurate and precise U/Pb and Th/Pb ages from Phanerozoic thorite, uranothorite and huttonite using LA-MC-ICPMS at the 5 mm spatial resolution. These phases have the potential to be robust chronometers in igneous and metamorphic rocks as well as to provide important provenance information complementary to more widely used minerals such as detrital zircon.

Despite efforts to understand the amorphization mechanisms of zeolites upon heating and subsequent dehydration, little is known about the extent of Si-Al disorder and topological variations in both crystalline and amorphous phases during amorphization. In this study, we investigated the atomic structure and the extent of configurational disorder (e.g., Si-Al ordering) in Na-zeolite A and other dehydrated phases during their temperature-induced amorphization using multi-nuclear solid-state NMR. We also report the first multi-nuclear ( 17 O, 29 Si, and 27 Al) NMR spectra of the intermediate amorphous phases. 29 Si MAS NMR results confirm the prevalence of amorphous phases up to ∼1073 K and variation in Q-species for the crystalline phases. The 27 Al quadrupolar coupling constant of the [4] Al peak in Nazeolite A and the intermediate amorphous phases increase with increasing temperature, which suggests an increase in the topological disorder associated with the structural distortion around [4] Al. 2D 17 O 3QMAS NMR spectra resolve the crystallographically distinct Si-O-Al sites in Na-zeolite A and three types of oxygen linkages namely, Si-O-Al, Si-O-Si, and Al-O-Al in the intermediate amorphous phases, which provides an unambiguous experimental evidence for an increase in the Si-Al disorder during the amorphization of zeolite. The detailed structural changes in Na-zeolite A and other dehydrated phases at various temperatures provide insights into the structural changes of other aluminosilicates during amorphization, thereby highlighting the changes in Si-Al ordering.

Pyrochlore-supergroup minerals containing relatively high Si concentration are quite common in various geochemical parageneses, e.g., carbonatites, alkaline syenites, pegmatites. However, the role of Si and the mechanism of its incorporation into the structure of these minerals, although widely discussed, have not been explained definitively. Our paper reports the results of comprehensive SEM, EPMA, XRD, TEM, and MAS-NMR studies performed for the first time on a natural pyrochlore, which is the late-magmatic to early hydrothermal accessory component of the nepheline syenite in the alkaline Mariupol massif in Ukraine. It represents partly metamict, patchy-zoned, A-cation depleted, REE-, U-, and Th-bearing fluornatropyrochlore, locally exceptionally rich in SiO 2 (up to 13.01 wt%) that underwent both primary and secondary alterations, leading to kenopyrochlore or hydropyrochlore species. The primary alteration was induced by high-temperature, Ca 2+ - and Si 4+ -rich, and F - moderate fluids, which affected only some domains of the pyrochlore crystals and resulted in filling the A site vacancies mainly by Ca 2+ , but also Mn 2+ , Sr 2+ , and K + . The secondary alteration, induced by the exposure of the host rock to ground water driving fluid-mediated coupled dissolution-reprecipitation process, affected the whole pyrochlore crystals (both Si-enriched and Si-free domains) and caused, among others, the leaching of some A- and Y-site components. TEM investigations indicate that the selected-area electron diffraction patterns taken from Si-poor areas show strong and sharp diffraction spots related to well-crystalline pyrochlore, whereas the Si-rich areas show weaker spots with a diffuse diffraction halo that are typical of metamict material. Due to the fact that no intergrowth with other Si-bearing phases was observed in the TEM images even at very high magnification, it might be concluded that Si 4+ can occupy severely a-decay damaged and chemically altered portions of this structure. The absence of Si in the sixfold-coordinated B site has been corroborated both by compositional relationships, and by the lack of any [6] Si 4+ signal around -200 ppm in the MAS-NMR spectrum. A broad signal in the spectrum appearing at around -84 ppm, points to an amorphous species with tetrahedrally coordinated Si, close to Q (2) species defined as Si atom with two bridging O atoms, i.e., [Si(OSi) 2 (-) 2 ], in the form of finite-length chain-like structures, located in the damaged A and B sites of the primary structure.

The present work reports the effects of g irradiation on vermiculite for the first time. The radiation-induced changes of vermiculite were studied using different techniques viz. ultravioletvisible spectroscopy (UV-Vis), dielectric measurements, X‑ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermoluminescence (TL). In UV-Vis analysis, the Cody model was employed to calculate structural disorder from Urbach energy, which explained the variation of the optical band gap (direct and indirect) with different (1-2000 kGy) γ doses. XRD analysis of the pristine and irradiated samples shows that the crystallinity improved upon irradiation at g dose up to 1000 kGy and deteriorated on further increase of the g dose. A significant change was observed in the dielectric properties after γ irradiation. Data shows that ac conductivity is proportional to the nth power of frequency (f n ) in pristine and irradiated vermiculite, with a slope n ranging between 0.52 and 0.76, which indicates that electronic conduction takes place through an electron hopping process. No appreciable changes in characteristic bands (FTIR) have been observed after irradiation, indicating that natural vermiculite is chemically stable. A well-defined TL peak around 132 °C and enhancement in its intensity with g dose (1-1000 kGy) make vermiculite a perfect thermoluminescence dosimeter and indicates usefulness applications in radiation dosimetry.

The ubiquity of quartz in continental crust, and the involvement of SiO2 in multiple metamorphic processes such as reactions, fluid flux, and solution-transfer processes, makes quartz an obvious choice for reconstructing prograde metamorphic conditions in various rock types. Recent studies have shown the usefulness of analyzing Ti distribution in quartz to constrain pressure-temperature-(relative) timedeformation (P-T-t-D) in metamorphosed tectonites. New high-precision single-crystal X‑ray diffraction volume constraints on Ti-doped and chemically pure quartz provide further evidence for substitution of Ti 4+ for Si 4+ in the tetrahedral site in quartz, with resultant lattice strain on the structure. Recent applications of the Ti-in-quartz thermobarometer to dynamically recrystallized quartz have identified recrystallized subgrains that contain lower Ti concentrations ([Ti]) than their host porphyroclasts. In addition, [Ti] are lower than expected for the temperatures of recrystallization. Atomistic simulations that estimate energetic perturbations resulting from Ti incorporation into the quartz lattice indicate that significant increases in strain energy occur only at very high [Ti]; the strain-energy increase is negligible for [Ti] typical of quartz grown under mid-crustal conditions. This suggests that lattice strain rarely provides an appreciable driving force for Ti loss from quartz; instead, it appears that subgrain boundaries and dislocation arrays migrating through recrystallizing quartz crystals can promote localized re-equilibration, thermodynamically regulated by the composition of the intergranular medium (typically undersaturated in Ti). It therefore appears that analyses from dynamically recrystallized quartz cannot be meaningfully interpreted until methods are developed that can account quantitatively for the reduction of Ti resulting from crystal plastic flow.

An equilibrium mixture of monoclinic pyrrhotite and pyrite was synthesized in the eutectic AlCl 3 - KCl melt at 525 K. The reaction 7FeS 2 (cr) + 12Ag(cr) = 8Fe 0.875 S(cr) + 6Ag 2 S(cr) was studied by an electromotive force technique in an all-solid-state electrochemical cell with an Ag + -conductive solid electrolyte in Ar at atmospheric pressure: (-) Pt | Ag | AgI | Ag 2 S, Fe 0.875 S, FeS 2 | Pt (+). In the 490-565 K temperature range a linear electromotive force vs. temperature trend was obtained from which the temperature dependence of the sulfur fugacity was determined for the monoclinic pyrrhotitepyrite equilibrium: logf S2 (mpo+py) = 14.079 - 14406⋅T -1 , (500 < T/K < 565). In addition, standard thermodynamic functions were calculated for monoclinic pyrrhotite Fe 0.875 S at 298 K and atmospheric pressure: ΔG f (mpo, 298.15 K) = -(136 200 ± 3000) J/mol, S°(mpo, 298.15 K) = (66.7 ± 1.3) J/(mol-K), ΔH f (mpo, 298.15 K) = -(157 400 ± 3000) J/mol. Gaseous sulfur, S 2 -ideal gas at 1 bar (10 5 Pa) pressure- was taken as a standard state for sulfur.

We investigated the properties of Al-bearing SiO 2 (with 4 or 6 wt% Al2O3) at pressures and temperatures corresponding to the lowermost mantle, using laser-heated diamond-anvil cell coupled with synchrotron-based in situ X-ray diffraction. The phase transition from CaCl 2 -structured to α-PbO 2 - structured (seifertite) polymorphs occurs between 113 and 119 GPa at 2500 K. The range of pressure where the two phases coexist is small. There is a slight decrease of the transition pressure with increasing Al-content. We propose a tentative phase diagram reporting the minerals composition as a function of pressure in the SiO 2 -Al 2 O 3 system. We also refine the P-V-T equation of state of Al-bearing seifertite based on volume measurements up to more than 160 GPa and 4000 K [V 0 = 92.73(10) Å 3 , K 0 = 304.2(3.0) GPa, K′ 0 = 4.59 (fixed), Θ D0 = 1130 K (fixed), γ 0 = 1.61(3)]. At 300 K, the volume decrease at the CaCl 2 to α-PbO 2 transition is 0.5(1)%, a value slightly lower than the 0.6% reported previously for Al-free samples. At high temperature, the Grüneisen parameter of seifertite is found to be similar to that of stishovite. Nevertheless, the ΔV/V across the CaCl 2 -form to seifertite transition is found to increase slightly with increasing temperature. Across the phase transition, volume changes can be translated into density changes only when the Al substitution mechanisms in both CaCl 2 -form and seifertite are defined. The analysis of all available data sets suggests different substitution mechanisms for the two SiO 2 polymorphs. Al-substitution could occur via O-vacancies in the CaCl 2 -form and via extra interstitial Al in seifertite. This would result in a density increase of 2.2(3)% at 300 K for SiO 2 in basaltic lithologies. Alternatively, the same Alsubstitution mechanism in both of the SiO 2 -dominated phases would yield a density increase of 0.5(1)%.

Nano-precipitates of Guinier-Preston zones (or G.P. zones) occur in slowly cooled orthopyroxenes (OPX). Due to their nanometer sizes and intergrowth with host OPX, both X-ray diffraction and highresolution TEM imaging cannot provide a consistent structure model for the G.P. zone precipitates. Combining Z-contrast imaging and density functional theory (DFT) methods, a correct crystal structure for the G.P. zone precipitates can be obtained, because Z-contrast imaging can reveal positions and occupancies of atoms directly. The crystal structure for the G.P. zone has P2 1 /c symmetry with 4 types of tetrahedral chains (OA1, OA2, OB, OC). The structure can be considered as periodic stacking of half unit cells of enstatite sub-layers and of diopside sub-layers in a twinning-like relationship along a-axis. The G.P. zones that precipitate out from their host Ca-bearing OPX at low temperature are metastable with respect to end-members of enstatite and diopside.

This paper explores the crystal chemical features of the bulk and the outermost (001) surface layers of two trioctahedral Li-rich mica-1M (space group C2) polytypes, i.e., a polylithionite (MLG-114) from Li-mica granitic pegmatite at St. Austell (SW England) and a Fe 2+ -rich polylithionite (Ch-140) from a rhyolite at Profitis Ilias, Chios Island, Greece. Structural formulas are [xii] (K 0.952 Na 0.019 Rb 0.019 ) [vi] (Al 1.034 Li 1.459 Fe 2+ 0.389 Fe 3+ 0.046 Mn 0.038 Mg 0.002 Zn 0.002 Ti 0.001 ) [iv] (Al 3+ 0.477 Si 3.523 )O 10.081 (F 1.735 OH 0.184 ) and [xii] (K 0.992 Na 0.014 ) [vi] (Al 0.980 Li 1.028 Fe 2+ 0.787 Fe 3+ 0.022 Mn 0.059 Mg 0.052 Zn 0.010 Ti 0.024 ) [iv] (Al 3+ 0.857 Si 3.143 ) O 10.095 (F 1.617 OH 0.288 ) for MLG-114 and Ch-140, respectively. Each mineral is characterized by a high F content in the anion site and has tetrahedral and octahedral compositions related to the exchange vector [vi] Li -1 [iv] Si -1 [vi] Fe 2+ [iv] Al. Unit-cell dimensions are a = 5.251(1), b = 9.066(2), c = 10.087(2) Å; β = 100.694(5)° for polylithionite MLG- 114 and a = 5.282(1), b = 9.121(3), c = 10.080(3) Å; β = 100.764(5)° for Ch-140. Crystal structure refinements (agreement factors are R = 3.58% and 3.75% for MLG-114 and Ch-140, respectively) demonstrate that the [vi] Li -1 [vi] Fe 2+ [iv] Si -1 [iv] Al exchange vector produces a decrease in the lateral dimensions of the tetrahedral and octahedral sheets. The decrease in basal oxygen distances results from the effect of the strain caused by the orientation of opposing tetrahedral sheets within a 2:1 layer. The decrease reduces the strain so that the basal oxygen plane can remain nearly planar. Changes in these dimensions via distortions of the tetrahedral basal-oxygen ring (α = 3.3° and 4.1° for MLG-114 and Ch-140, respectively) are limited. Octahedral M1 and M3 sites are similar in size and much larger than M2 and the mean electron count is M3 < M1 < M2 in MLG-114 and M1 ≈ M2 < M3 in Ch-140. Al preferentially occupies the M2 site, whereas Fe and Li are nearly disordered between M1 and M3 sites with a slight preference of Fe for the M1 site in MLG-114 and for M3 site in Ch-140. Element concentrations on the (001) surface, obtained through X‑ray photoelectron spectroscopy (XPS) high-resolution spectra for Si 2p , Al 2p , Fe 2p , K 2p , Li 1s , and F 1s core levels, indicate that a greater amount of lithium and a smaller amount of potassium characterize the surface with respect to the bulk. The decrease in K content, commonly observed in micas, is related to its location on the cleavage surface, because the cation must be distributed equally between the two (001) surfaces generated upon cleavage. The increase in Li content on or near the (001) cleavage surface suggests a preference for cleavage near lithium-enriched regions. The surface structure of the polylithionite crystals suggests that Al, Li, and Fe cations maintain coordination features at the surface similar to the bulk. Silicon, however, which is generally in fourfold coordination, shows also a small number of [1]-fold coordinated components at a binding energy of 99.85 eV.

Hibonite single crystals were synthesized using two different techniques: hot-pressing of polycrystalline hibonite by means of piston-cylinder apparatus and solid state reaction using citrate-based sol-gel precursors. Chemical analyses, UV/Vis spectroscopy, and single-crystal X-ray characterization were performed on four sets of Ti-Mg-bearing hibonites to investigate the substitution mechanism of Ti 3+ , Ti 4+ , and Mg 2+ , relevant for hibonites found in calcium-aluminum-rich inclusions in meteorites. The unit-cell volume of hibonite depends linearly on the concentration of Ti and Mg: V = 8.21(3)·(Ti tot + Mg) apfu + 586.06(1). Structural refinements, carried out in the space group P6 3 /mmc, demonstrate that Ti occupies two sites: M2, a trigonal bipyramid, and M4, a distorted octahedron occurring in facesharing pairs. The Ti occupancy factor was refined at both sites. Due to the repulsion of neighboring Ti cations the bond distance M4-O3 increases with increasing Ti content and the cations are displaced from the central position of the polyhedron. The displacement factors (U 33 ) M2 and the site occupancy factor for Ti in the M2 site positively correlate for the samples, which have more than 0.3-0.4 Ti apfu , while (U 33 ) M2 remains that of pure hibonite for small Ti occupancies at the M2 site. This plateau of displacement factor reflects the local strain fields around the substituted Ti atoms and its magnitude indicates that these strain fields begin to overlap at a Ti-Ti separation of about 1-2 unit cells. For a sample synthesized at low oxygen fugacity we detected Ti 3+ by means of UV/Vis absorption spectroscopy. The presence of Ti 3+ has a clear effect on the M4-M4 distance, which deviates from the linear trend described by samples containing mainly Ti 4+ . The average bond length M3-O depends linearly on the Mg content of these synthetic hibonites clearly indicating that Mg occupies this site.

Minor-element concentrations in marine ferromanganese nodules are primarily controlled by the mineralogy, which itself depends on redox conditions at the sediment-water interface. Results are presented for the first in-depth X-ray microstructural and microspectroscopic investigation of a mixed hydrogenetic-diagenetic nodule, which is representative of ferromanganese deposits on abyssal plains. The measurements were conducted by micro-X-ray diffraction and X-ray absorption spectroscopy (both XANES and EXAFS) on hydrogeneous and diagenetic regions of the nodule. The hydrogeneticdiagenetic interface was imaged by X-ray microfluorescence, after which regions of interest were chosen to represent mineralogical and chemical transformations that occurred at the early stage of suboxic diagenesis. In the hydrogenetic nodule (oxic environment), Mn is speciated as Fe-vernadite, a nanocomposite material composed of intergrown feroxyhite (δ-FeOOH) and monodispersed phyllomanganate layers having no interlayer Mn (vernadite). In the diagenetic nodule (suboxic environment), Mn is speciated dominantly as Mg-rich 10 Å vernadite, which consists of a random intergrowth of vernadite and its transformation product todorokite. The authigenic 10 Å vernadite precipitated from the components of vernadite in Fe-vernadite that were dissolved in suboxic microenvironments of the sediment. Direct evidence supporting a redox-driven dissolution reaction is provided by the valence composition of Mn, as measured by micro-XANES, which is 0.69Mn 4+ + 0.24Mn 3+ + 0.07Mn 2+ (average = 3.62 ± 0.04 v.u.) for Fe-vernadite and 0.61Mn 4+ + 0.23Mn 3+ + 0.16Mn 2+ (average 3.28 ± 0.04 v.u.) for 10 Å vernadite. Ni and Cu, derived mainly from dissolved vernadite and oxidized organic matter, replace structural Mn 3+/4+ in both the MnO 2 layer and todorokite domains of 10 Å vernadite. Pure todorokite in highly diagenetic regions of the nodule has an average formula of Mg 2+ 0.167 (Mn 4+ 0.783 Mn 3+ 0.099 Co 3+ 0.002 Ni 2+ 0.076 Cu 2+ 0.040 )O 2 ·nH 2 O, with an atomic ratio of (Cu+Ni+Co)/Mn = 0.13, which is slightly lower than 0.167 (⅙), the maximum metal uptake capacity reported for marine nodules. By analogy with synthetic todorokites we infer that Mg 2+ , which has a hydrated diameter close to that of the [3 × 3] tunnel size of todorokite, and Mn 3+ and Cu 2+ , which prefer Jahn-Teller distorted octahedra, play a crucial role in templating the topotactic transformation of 10 Å vernadite to todorokite and stabilizing todorokite in suboxic marine sediments.

Agakhanovite-(Y), ideally (YCa)⃞2KBe 3 Si 12 O 30 , is a new milarite-group mineral from the Heftetjern pegmatite, Tørdal, southern Norway. Crystals are prismatic along [001], and show the forms {100} and {100}. Agakhanovite-(Y) is colorless with a white streak and a vitreous luster, and does not fluoresce under ultraviolet light. There is no cleavage or parting, and no twinning was observed. Mohs hardness is 6, and agakhanovite-(Y) is brittle with a conchoidal fracture. The calculated density is 2.672 g/cm 3 . Optical properties were measured with the Bloss spindle stage for the wavelength 590 nm using a gel filter. Agakhanovite-(Y) is uniaxial (-) with indices of refraction w = 1.567, e = 1.564, both ±0.002; the calculated birefringence is 0.003 and it is non-pleochroic. Agakhanovite-(Y) is hexagonal, space group P6/mcc, a = 10.3476(2), c = 13.7610(3) Å, V = 1276.02(9) Å 3 , Z = 2, c:a = 1.330. The seven strongest lines in the X-ray powder-diffraction pattern are as follows: d (Å), I, (hkl): 2.865, 100, (1̅24); 3.287, 96, (1̅31); 4.134, 84, (1̅22); 6.877, 56, (002); 2.986, 43, (030); 4.479, 38, (020); 2.728, 36, (024). Chemical analysis by electron microprobe gave SiO 2 69.56, Al 2 O 3 0.35, Y 2 O 3 9.69, Yb 2 O 3 0.15, FeO 0.02 CaO 5.75, Na 2 O 0.07, K 2 O 4.52, BeO(calc) 7.06, H 2 O(calc) 1.74, sum 98.91 wt%. The H 2 O content was determined by crystal-structure analysis. On the basis of 30 anions, the empirical formula is (Y 0.89 Yb 0.01 Ca 1.06 )S 1.96 (H 2 O) 0.92 Na 0.02 K 1.00 (Be 2.93 Al 0.07 )S 3.00 Si 12.02 O 30 . The crystal structure of agakhanovite-(Y) was refined to an R 1 index of 1.9% based on 660 unique observed reflections collected on a three-circle rotating-anode (MoKa X-radiation) diffractometer equipped with multilayer optics and an APEX-II detector. In the end-member structure of agakhanovite-(Y), the A site is occupied equally by Y and Ca, and the B site is vacant; agakhanovite-(Y) is the Y-analog of oftedalite: ScCa⃞ 2 KBe 3 Si 12 O 30 , and the Y-Ca-Be analog of klöchite, (Fe 2+ Fe 3+ )⃞ 2 KZn 3 Si 12 O 30 .

The new mineral species ichnusaite, Th(MoO 4 ) 2 ·3H 2 O, has been discovered in the Mo-Bi mineralization of Su Seinargiu, Sarroch, Cagliari, Sardinia, Italy. It occurs as colorless thin {100} tabular crystals, up to 200 μm in length, associated with muscovite, xenotime-(Y), and nuragheite, Th(MoO 4 ) 2 ·H 2 O. Luster is pearly adamantine. Ichnusaite is brittle, with a perfect {100} cleavage. Owing to the very small quantity of available material and its intimate association with nuragheite, density and optical properties could not be measured. Electron microprobe analysis gave (mean of 4 spot analyses in wt%): MoO 3 47.86(1.43), ThO 2 43.40(79), total 91.26(87). On the basis of 8 O atoms per formula unit and assuming 3 H 2 O groups, in agreement with the crystal structure data, the chemical formula of ichnusaite is Th 0.99 Mo 2.01 O 8 ·3H 2 O. Main diffraction lines, corresponding to multiple hkl indices, are [d(Å), relative visual intensity]: 5.66 (m), 3.930 (m), 3.479 (s), 3.257 (s), 3.074 (m). Ichnusaite is monoclinic, space group P2 1 /c, with a = 9.6797(12), b = 10.3771(13), c = 9.3782(12) Å, β = 90.00(1)°, V = 942.0(2) Å 3 , Z = 4. The crystal structure has been solved and refined to a final R 1 = 0.051 on the basis of 2008 observed reflections [with F o > 4σ(F o )]. It consists of electroneutral [Th(MoO 4 ) 2 (H 2 O) 2 ] 0 (100) sheets of polymerized ThO 7 (H 2 O) 2 and MoO 4 polyhedra; successive sheets, stacked along [100], are connected through hydrogen bonds. Ichnusaite brings new understanding about the crystal chemistry of actinide molybdates, that may form during the alteration of spent nuclear fuel and influence the release of radionuclides under repository conditions.

Analysis of radiation damage in natural mineral analogs such as zircon is important for the evaluation of the long-term behavior of nuclear waste forms and for geochronology. Here we present results of experiments to determine the partitioning of radiation damage due to the heavy nuclear recoil of uranium and thorium daughters and the a-particles ejected in an α-decay event in zircon. Synthetic polycrystalline zircon ceramics were doped with 10 B and irradiated in a slow neutron flux for 1, 10, and 28 days to achieve the reaction 10 B + n → 7 Li + α (+2.79 MeV), creating an α event without a heavy nuclear recoil. The 7 Li atoms produced in the nuclear reaction were directly detected by NMR “spin-counting”, providing a precise measurement of the α-dose applied to each sample. The amount of damage (number fraction and volume fraction) created by each α-event (one α-event being a 7 Li + α-particle) has been quantified using radiological nuclear magnetic resonance and X-ray diffraction data. The number of permanently displaced atoms in the amorphous fraction was determined by 29 Si NMR to be 252 ± 24 atoms for the 10 B(n,α) event when the heavy recoil is absent, which is broadly in agreement with ballistic Monte Carlo calculations. The unit-cell swelling of the crystalline fraction, determined by X-ray diffraction, is small and anisotropic. The anisotropy is similar to that observed in ancient natural samples and implies an initial anisotropic swelling mechanism rather than an anisotropic recovery mechanism occurring over geological timescales. The small unit-cell volume swelling is only ∼6% of the expansion frequently attributed to α-particles associated with an actinide α-decay event. The lattice parameters indicate a volume increase as a function of a dose of 0.21 A 3 /10 18 α-events/g, which is significantly less than the increase of 3.55 A 3 /10 18 α-events/g seen in Pu-doped zircon and 2.18 A 3 /10 18 α-events/g seen in natural zircon. It is concluded that the heavy recoil plays a more important role in unit-cell swelling than previously predicted. The likely mechanism for such an effect is the rapid, and thus defect-rich, recrystallization of material initially displaced by the heavy recoil.

This study of the spectral properties of Ca-sulfates was initiated to support remote detection of these minerals on Mars. Gypsum, bassanite, and anhydrite are the currently known forms of Ca-sulfates. They are typically found in sedimentary evaporites on Earth, but can also form via reaction of acidic fluids associated with volcanic activity. Reflectance, emission, transmittance, and Raman spectra are discussed here for various sample forms. Gypsum and bassanite spectra exhibit characteristic and distinct triplet bands near 1.4-1.5 μm, a strong band near 1.93-1.94 μm, and multiple features near 2.1-2.3 μm attributed to H 2 O. Anhydrite, bassanite, and gypsum all have SO 4 combination and overtone features from 4.2-5 μm that are present in reflectance spectra. The mid-IR region spectra exhibit strong SO 4 ν 3 and ν 4 vibrational bands near 1150-1200 and 600-680 cm -1 (∼8.5 and 16 μm), respectively. Additional weaker features are observed near 1005-1015 cm -1 (∼10 μm) for ν 1 and near 470-510 cm -1 (∼20 μm) for ν 2 . The mid-IR H 2 O bending vibration occurs near 1623-1630 cm -1 (∼6.2 μm). The visible/near-infrared region spectra are brighter for the finer-grained samples. In reflectance and emission spectra of the mid-IR region the ν 4 bands begin to invert for the finer-grained samples, and the ν 1 vibration occurs as a band instead of a peak and has the strongest intensity for the finer-grained samples. The ν 2 vibration is a sharp band for anhydrite and a broad peak for gypsum. The band center of the ν 1 vibration follows a trend of decreasing frequency (increasing wavelength) with increasing hydration of the sample in the transmittance, Raman, and reflectance spectra. Anhydrite forms at elevated temperatures compared to gypsum, and at lower temperature, salt concentration, and pH than bassanite. The relative humidity controls whether bassanite or gypsum is stable. Thus, distinguishing among gypsum, bassanite, and anhydrite via remote sensing can provide constraints on the geochemical environment.

The biological cycling of phosphorus on Earth could be as early as the origin of life in early Archean. However, because of the low abundance and fine particle size, phosphate related to microbial ecophysiological activities in early sedimentary rocks, especially those deposited before the Great Oxidation Event (GOE, ca. 2.45-2.32 Ma), is still poorly addressed. It is not until recently that certain petrographic and mineralogical features of apatite in the early Precambrian sedimentary rocks were found related to microbial activities. In this study, we report high-resolution electron microscopic investigations on apatite from the Neoarchean to early Paleoproterozoic banded iron formations (BIFs), Mesoproterozoic to Lower Cambrian black shale and phosphorites, and Pliocene sediments. Apatite in BIFs occurs as 4-8 mm radial flowers with “petals” made of apatite rods. Their mineralogical and petrologic features are highly similar to those in the younger sedimentary rocks in which biomass have been confirmed to play an important role in the mineralization of phosphate. We suggest that these sedimentary rocks or sediments have experienced similar phosphogenetic processes mediated by biomass that led to the mineralization of phosphorus. The formation and preservation of phosphate (apatite) with conspicuous recognizable features in association with biological activities from Late Archean to Pliocene implies its universal significance in recording microbial processes through deep geological evolution. With mild dynamic processes, the martian (sub)surface has better preservation conditions than Earth, and the micro-structure of phosphate formed in environments mediated by microorganisms could be recognized by high-resolution observations on the surface of Mars or returned samples, if microbial life ever developed on Mars.

Gypsum is a mineral that commonly precipitates in hydrothermal environments. This study reports the electron microscopic analyses of gypsum morphologies and crystal sizes found in hot springs on the Kamchatka Peninsula, Russia, and compares these analyses with gypsum morphologies of hydrothermal genesis found in Lower Cambrian black shale. In sediments of the Kamchatka hot springs, we observed prismatic, prismatic pseudo-hexagonal, fibrous, tubular, lenticular and twinned gypsum crystals, with crystal sizes ranging from <200 nm to >200 μm. The coexistence of diverse crystal habits of gypsum implies a constant interaction between hot spring geochemistry and the metabolisms of the microbial community. The crystallization of Ca- and Ba-sulfates in the black shale of the Lower Cambrian, which shows similar but less varied morphology, was influenced by post-depositional hydrothermal fluids. The partial replacement of pyrite by sulfates in a situation coexisting with rich biomass deposits and animal fossils indicates limited modification of the sedimentary records by biological materials. If the gypsum precipitated on Mars underwent similar interactions between microbial communities and their geochemical environments, the resulting crystal habits could be preserved even better than those on Earth due to the weak geodynamics prevailing on Mars throughout its evolutionary history.

Experimental and theoretical evidence for the coupled substitution of B and H in synthetic forsterite and a natural olivine is presented. The intensities of OH bands at 3704 cm -1 (//z), 3598 cm -1 (//x,y), and 3525 cm -1 (//x) in a heterogeneous B-doped synthetic forsterite crystal matches the zoning of B concentration measured by ion probe. The two anti-symmetric stretching vibrations of BO 3 groups occur at 1301 cm -1 (//x) and 1207 cm -1 (//z) for the 10 B and at 1256 and 1168 cm -1 for the 11 B isotope. A microscopic model of the mixed (B,H) defect that accounts for experimental observations is obtained from quantum mechanical calculations. The BO 3 group lies on the (O3-O1-O3) face of the vacant Si site and the H atom is bonded to the O2 atom at the remaining apex. The occurrence of the same OH bands associated with v 3 BO 3 vibrations in a natural olivine sample from Pakistan confirms the occurrence of this defect in nature. The three diagnostic OH bands can be used as a signature of H associated with boron substitution in olivine and forsterite, leading to a quantitative analysis of their contribution to H-defects.

The structures of high-pressure magmatic liquids have often been inferred from spectroscopic studies on quenched and decompressed glasses. However, it has not been completely verified whether the structures of quenched and decompressed glasses are representative of the structure of their corresponding liquids at the glass transition temperature and synthesis pressure. Here, we provide quantitative evidence for the retention of pressure-induced configurational changes upon isobaric quench and isothermal decompression for synthesis pressures up to 3.5 GPa. We use the degree of densification and elastic compressibility of permanently densified glasses, together with thermo-elastic data from the literature, to calculate the density of the melt at the glass transition temperature and synthesis pressure. The derived densities agree with those derived directly from the thermal equations of state of the melts. This observation indicates that, at least up to 3.5 GPa, the densified structure of the melt is preserved in the glass upon quenching and decompression; this validates past and future structural studies of high-pressure melts based on studies of quenched and decompressed glasses.

Minerals trapped as inclusions within other host minerals can develop residual stresses on exhumation as a result of the differences between the thermo-elastic properties of the host and inclusion phases. The determination of possible entrapment pressures and temperatures from this residual stress requires the mutual elastic relaxation of the host and inclusion to be determined. Previous estimates of this relaxation have relied on the assumption of linear elasticity theory. We present a new formulation of the problem that avoids this assumption. We show that for soft inclusions such as quartz in relatively stiff host materials such as garnet, the previous analysis yields entrapment pressures in error by the order of 0.1 GPa. The error is larger for hosts that have smaller shear moduli than garnet.