Volume 100, Issue 4

The Curiosity rover on Mars, landed in 2012, is capable of mineralogical investigation using X‑ray diffraction, complementing the abundant infrared remote sensing data already available on clay minerals. We can, however, expect that the in situ X‑ray diffraction information will convey a more complex picture than that inferred from infrared spectroscopy alone. CheMin has landed.

The paper entitled “Tweed, Twins, and Holes,” by Ekhard K.H. Salje [2015, vol. 100(2-3)] gives a comprehensive overview on experiments, theory, and computer simulations of microstructures in ferroelastic and multiferroic minerals and synthetic crystals, with special emphasis on domain wall properties. Such materials are highly interesting for technological applications as well as from a more fundamental point of view, bearing a lot of open questions. Domain boundaries are nanometer-sized objects that very often exhibit physical properties quite different from the bulk. This can lead to completely new functionalities as compared to single domain crystals.

Most silicate melt inclusions (MI) contain bubbles, whose significance has been alternately calculated, pondered, and ignored, but rarely if ever directly explored. Moore et al. (2015) analyze the bubbles, as well as their host glasses, and conclude that they often hold the preponderance of CO2 in the MI. Their findings entreat future researchers to account for the presence of bubbles in MI when calculating volatile budgets, saturation pressures, and eruptive flux.

Mineralogy is both a basic and applied discipline, basic in understanding, on the atomic scale, the structure, properties, and reactivity of minerals and applied in its relevance to geology, planetary processes, environmental issues, and materials in the broader sense. This article is a 2015 snapshot of the interrelations and opportunities linking mineralogy and such other fields. The emphasis is on showing how relevant, indeed essential, mineralogy is to the stewardship of our planet in the broadest sense.

Understanding the dynamics of biomineral growth is a challenging goal of biomineralogy that can be achieved in part by deciphering biomineral structures and chemistries. The morphology, structure, and chemistry of six skeletons of Corallium and Paracorallium species (C. rubrum, C. elatius, C. johnsoni, C. niobe, P. japonicum, and P. thrinax) from the Mediterranean, the Atlantic, and the Pacific oceans have been studied by X-ray micro-computed tomography, polarized light microscope, scanning electron microscope, and electron microprobe. All species have two types of biomineral structures: an inner skeleton and sclerites that are small grains of Mg-calcite found in the living tissues surrounding the skeleton. All skeletons display a central core surrounded by an annular domain. In the species studied by electron microprobe (C. rubrum, C. elatius, and P. japonicum), the central core and the annular domains display different chemical compositions with the core richer in magnesium and poorer in sulfur than the annular domain. In terms of structure, special emphasis has been put on central cores for which little data are available. The central cores are made of sclerites and sclerite aggregates within a cement consisting of fine layers of Mg-calcite. On the other hand, the annular parts are made of fine concentric layers of calcite crystallites with only rare sclerites. These contrasting features imply two different growth modes: (1) a “block and cement” mode taking place at the apex of a branch and associated with a fast axial growth rate (~2 mm/yr); and (2) a layer-by-layer mode occurring below the apex and associated with a slow radial growth (~0.2 mm/yr). The change from a growth mode to another is anatomically controlled by the presence of a continuous network of gastrodermal canals around the sub-apical skeleton, preventing to a large extent the aggregation of sclerites. It is generally accepted that the Coralliidae family exhibits different types of skeletogeneses. In contrast with this idea, we observe that all studied Corallium species display remarkable similarities in terms of skeletogenesis and a unifying growth model for the Corallium genus is proposed. Similarities and differences with previous models are discussed. The present study shows that the morphological criterion initially used to establish the genus Paracorallium in the Coralliidae family is inadequate.

The patterns of linkage of chemical bonds in space contain significant energetic information that may be used as the basis of a theoretical approach to the structure and chemical composition of minerals. This approach combines aspects of graph theory, bond-valence theory, and the moments approach to the electronic-energy density-of-states to interpret topological aspects of crystal structures, and allows consideration of many issues of crystal structure, mineral composition, and mineral behavior that are not addressed by established theoretical methods. The chemical composition of a mineral is controlled by the weak interaction between the structural unit and the interstitial complex. The principle of correspondence of Lewis acidity-basicity asserts that stable structures will form when the Lewisbase strength of the structural unit closely matches the Lewis-acid strength of the interstitial complex. This principle allows analysis of the factors that control the chemical compositions and aspects of the structural arrangements of minerals, and provides a mechanism to understand the relations between structure, the speciation of its constituents in aqueous solution, and its mechanism of crystallization. (H 2 O) groups in the structural unit limit the polymerization of the structural unit in one or more directions, controlling the polymerization of the structural unit. This is a major cause of structural diversity in oxygen-based minerals, and accounts for the systematic distribution in mineral species from the core to the surface of the Earth. The moments approach to the electronic-energy density-of-states provides a bond-topological interpretation of the energetics of a structure. When comparing structures, the most important structural differences involve the first few disparate moments of the electronic-energy density-of-states. We may classify chemical reactions according to the lowest-order moment of the electronic-energy density-ofstates that is conserved, which allows us to identify the principal structural changes that drive chemical change: (1) coordination number for discontinuous reactions, and (2) short-range order for continuous reactions. This relation between the bond topology of a structure and its enthalpy of formation from constituent oxides is indicated by a correlation between change in anion-coordination number and reduced enthalpy of formation for the reactions [6] Mg m [4] SinO (m+2n) = mMgO+nSiO 2 .

The lithium aluminosilicate mineral petalite (LiAlSi 4 O 10 ) has been studied with high-pressure single-crystal X-ray diffraction (HP-XRD) up to 5 GPa. Petalite undergoes two fully reversible pressure-induced first-order phase transitions, not previously reported in the literature, at ca. 1.5 and 2.5 GPa. The first of these transforms the low-pressure α-phase of petalite (P2/c) to an intermediate β′-phase that then fully converts to the high-pressure β-phase at ca. 2.5 GPa. The α → β transition is isomorphic and is associated with tripling of the unit-cell volume. Analysis of the HP-XRD data show that although the fundamental features of the petalite structure are retained through this transition, there are subtle alterations in the internal structure of the silicate double-layers in the β-phase relative to the α-phase. Measurement of the unit-cell parameters of petalite as a function of pressure, and fitting of the data with third-order Birch-Murnaghan equation of state, has provided revised elastic constants for petalite. The bulk moduli of the α- and β-phases are 49(1) and 35(3) GPa, respectively. These values indicate that the compressibility of the α-phase of petalite lies between those of the alkali feldpsars and alkali feldspathoids, whereas the β-phase has a compressibility more comparable with layered silicates. Structure analysis has shown that the compression of the α-phase is facilitated by the rigid body movement of the Si 2 O 7 units from which the silicate double-layers are constructed.

The August 7-8, 2008, eruption of Kasatochi Island volcano, located in the central Aleutians Islands, Alaska, produced abundant, compositionally heterogeneous basaltic andesite (52-55 wt% SiO 2 ) that has been interpreted to result from pre-eruptive magma mixing. The basaltic andesite contains two populations of plagioclase phenocrysts. The first, volumetrically dominant population consists of oscillatory-zoned phenocrysts with an overall normal zonation trend toward comparatively sodic rims (An 55-65 ), interrupted by dissolution features and spikes in calcium content (up to ~An 85 ). The second population consists of phenocrysts with highly calcic compositions (~An 90 ). These phenocrysts contain sharp decreases in calcium content close to their rims (reaching as low as ~An 60 ), but are otherwise texturally and compositionally homogeneous. Groundmass plagioclase microlites are generally much more calcic than rims of the first phenocryst population, with more than 50% of measured microlites containing >An 80 . Major, minor, and trace element concentrations of plagioclase microlites and phenocrysts indicate that oscillatory-zoned phenocrysts derived from cooler (800-950 °C), more silicic mixing magma, while unzoned, calcic phenocrysts were associated with hotter (900-1050 °C), mafic magma. The mixing of these magmas just prior to eruption, followed by decompression during the eruption itself created high effective undercoolings in the mafic end-member, and lead to the nucleation of high-An microlites. MgO and FeO concentrations of plagioclase microlites and high-An phenocryst rims (up to ~0.4 and ~1.3 wt%, respectively) provide further evidence for high mixing- and eruptioninduced effective undercoolings.

The ferric oxyhydroxide minerals akaganéite and schwertmannite are associated with acidic environments and iron alteration on Earth and may be present on Mars as well. These minerals have a tunnel structure and are crystallographically related. The extended visible region reflectance spectra of these minerals are characterized by a broad Fe 3+ electronic transition centered near 0.92 μm, a reflectance maximum near 0.73 μm, and a shoulder near 0.59 μm. The near-infrared (NIR) reflectance spectra of each of these minerals are dominated by broad overtones and combinations of the H 2 O vibration features. These occur near 1.44-1.48 and 1.98-2.07 μm (∼6750-6950 and 4830-5210 cm -1 ) in akaganéite spectra, while in schwertmannite spectra they occur at 1.44-1.48 and 1.95-2.00 μm (∼6750-6950 and 5005-5190 cm -1 ). Additional bands due to OH vibrational overtones are found near 1.42 μm (∼7040 cm -1 ) in akaganéite and schwertmannite spectra and due to OH combination bands in akaganéite spectra at 2.46 μm (4070 cm -1 ) with weaker components at 2.23-2.42 μm (4134-4492 cm -1 ). A strong and broad band is observed near 2.8-3.1 μm (∼3300-3600 cm -1 ) in reflectance and transmittance spectra of akaganéite and schwertmannite due to overlapping OH and H 2 O stretching vibrations. H 2 O bending vibrations occur near 1620 cm -1 (∼6.17 μm) in akaganéite spectra and near 1630 cm -1 (∼6.13 μm) in schwertmannite spectra with additional bands at lower frequencies due to constrained H 2 O molecules. OH bending vibrations occur near 650 and 850 cm -1 (∼15.4 and 11.8 μm) in akaganéite spectra and near 700 cm -1 (∼14.3 μm) in schwertmannite spectra. Sulfate vibrations are observed for schwertmannite as a ν 3 triplet at 1118, 1057, and 1038 cm -1 (∼8.9, 9.5, and 9.6 μm), ν 1 at 982 cm -1 (∼10.2 μm), ν 4 near 690 cm -1 (∼14.5 μm), and ν 2 at 608 cm -1 (∼16.5 μm). Fe-O bonds occur near 410-470 cm -1 (μm) for akaganéite and schwertmannite. Both minerals readily absorb H 2 O molecules from the environment and adsorb them onto the mineral surfaces and incorporate them into the tunnels. If akaganéite and schwertmannite were present on the surface of Mars they could enable transport of H 2 O from the near-surface to the atmosphere as the partial pressure of H 2 O varies diurnally.

We present a numerical modeling approach to infer timescales of the exhumation and cooling history recorded in the chemical composition of minerals in a garnet pyroxenite from the Granulitgebirge, Saxony/Germany. The studied sample contains remarkable exsolution textures from former megacrysts that produced up to millimeter-wide, alternating lamellae of garnet (Grt) and clinopyroxene (Cpx). Compositional profiles of major and minor elements measured with the electron microprobe perpendicular to the Grt-Cpx interfaces reveal systematic zoning patterns for Fe, Mg, Al, Si, Cr, Ti in clinopyroxene and Ca, Fe, Mg, Mn in garnet, respectively. In addition to simple thermal modeling that is used to constrain the conditions of emplacement of the Granulitgebirge Massif at shallow crustal levels, we combine thermodynamic data with a numerical finite difference scheme that simulates growth and simultaneous diffusive exchange between garnet and clinopyroxene along a virtual cooling path. The latter model assumes local equilibrium at the interface. Diffusive fluxes are constrained by mass balance. It is shown that zoning patterns such as Fe-Mg exchange between garnet and clinopyroxene can be used to extract cooling rates and thus timescales of exhumation, while the profiles for the minor elements are provisionally related to the growth history of the lamellae. Furthermore, zoning profiles in the lamellae can only be reproduced with ultrahigh cooling rates similar to contact metamorphic conditions. This in turn, suggests that the massif was emplaced at temperatures above 900 °C in agreement with the observed spatial extent of a contact aureole within low-grade metasedimentary rocks surrounding the granulite massif as predicted by thermal modeling. Exhumation of the massif without cooling below 900 °C requires an exhumation rate of several centimeters per year. Thus, we propose an almost isothermal exhumation period of ~1 Ma followed by isobaric cooling from 900 to 600 °C within less than 10 ka.

Major and trace element and volatile compositions of reheated melt inclusions (RMI) and their clinopyroxene hosts from a selected “sub-effusive” nodule from the uppermost layer of the Sarno (Pomici di Base; PB) plinian eruption of Mt. Somma-Vesuvius (Italy) have been determined. The Sarno eruption occurred during the first magmatic mega-cycle and is one of the oldest documented eruptions at Mt. Somma-Vesuvius. Based on RMI and clinopyroxene composition we constrain processes associated with the origin of the nodule, its formation depth, and hence the depth of the magma chamber associated with the Sarno (PB) eruption. The results contribute to a better understanding of the early stages of evolution of the long-lived Mt. Somma-Vesuvius volcanic complex. The crystallized MI were heated to produce a homogeneous glass phase prior to analysis. MI homogenized between 1202-1256 °C, and three types of RMI were distinguished based on their compositions and behavior during heating. Type I RMI is classified as phono-tephrite-tephri-phonolite-shoshonite, and is the most representative of the melt phase from which the clinopyroxenes crystallized. The second type, referred to as basaltic RMI, have compositions that have been modified by accidentally trapped An-rich feldspar and/or by overheating during homogenization of the MI. The third type, referred to as high-phosphorus (high-P) RMI, is classified as picro-basalt and has high-P content due to accidentally trapped apatite. Type I RMI are more representative of magmas associated with pre-Sarno eruptions than to magma associated with the Sarno (PB) eruption based on published bulk rock compositions for Mt. Somma-Vesuvius. Therefore, it is suggested that the studied nodule formed from a melt compositionally similar to that which was erupted during the early history of Mt. Somma. The clinopyroxene and clinopyroxene-silicate melt thermobarometer models suggest minimum pressures of 400 MPa (~11 km) for nodule formation, which is greater than pressures and depths commonly reported for the magmas associated with younger plinian eruptions of Mt. Somma-Vesuvius. Minimum pressures of formation based on volatile concentrations of MI interpreted using H 2 O-CO 2 -silicate melt solubility models indicate formation pressures ≤300 MPa.

We present a suite of 36 high-temperature (900-1100 °C) experiments performed on 10 × 10 mm unjacketed cores of rhyolitic obsidian from Hrafntinnuhryggur, Krafla, Iceland, under atmospheric pressure. The obsidian is bubble- and crystal-free with an H 2 O content of 0.11(4) wt%. The obsidian cores were heated above the glass transition temperature (T g ), held for 0.25-24 h, then quenched. During each experiment the volume of the samples increased as H 2 O vapor-filled bubbles nucleated and expanded. Uniquely, the bubbles did not nucleate on the surface of the core, nor escape, conserving mass during all experiments. Within each isothermal experimental suite, the cores increased in volume with time until they reached a maximum, after which continued heating caused no change in volume (measured by He-pycnometry). We interpret these T-t conditions as representing thermochemical equilibrium between the melt and exsolved vapor. These experiments are modeled to recover the 1-atm, temperature-dependent solubility of water in the rhyolite melt. Our results define the magnitude of retrograde solubility (-7.1 × 10 -3 wt% H 2 O per 100 °C) and provide estimates of the enthalpy and entropy of the H 2 O exsolution reaction [ΔH° = 17.8 kJ/mol, ΔS° = 107 J/(K·mol)]. We conclude by modeling the implications of retrograde solubility for the glass transition temperatures (T g ) of cooling volcanic systems at pressures relevant to volcanic conduits and the Earth’s surface. All volcanic systems cool; the effects of retrograde solubility are to allow melts to rehydrate by H 2 O dissolution as they cool isobarically, thereby depressing T g and expanding the melt window. Ultimately, the melt is quenched at higher H 2 O contents and lower temperatures where the isobaric retrograde solubility curve “catches” the evolving T g .

The H 2 O and CO 2 contents of melt inclusions can potentially be used to infer pressures of crystallization and inclusion entrapment because the solubility of mixed H 2 O-CO 2 vapor has been determined experimentally for a wide range of melt compositions. However, melt inclusions commonly develop a shrinkage bubble during post-entrapment cooling and crystallization because these processes cause a pressure drop in the inclusion. This pressure drop causes a vapor bubble to nucleate, leading to exsolution of low-solubility CO 2 from the trapped melt. To investigate the loss of CO 2 into such bubbles, we experimentally heated large, naturally glassy melt inclusions in olivine (Fo contents of 88.1 ± 0.2) from a Mauna Loa picrite to rehomogenize the inclusions. Rapid heating to 1420 °C using a hightemperature heating stage dissolved the shrinkage bubbles into the melt. CO 2 contents measured by FTIR spectroscopy and recalculated for melt in equilibrium with the olivine host are 224-505 ppm (n = 11) for heated inclusions, much higher than the CO 2 contents of naturally quenched inclusions from the same sample (38-158 ppm; n = 8). Pressures of inclusion entrapment calculated from the H 2 O and CO 2 data for the heated inclusions range from 0.5 to 1.1 kbar, indicating that Mg-rich olivine crystallized at very shallow depths beneath the surface of Mauna Loa. Our results indicate that 40-90% (average 75%) of the original CO 2 dissolved in the melt at the time of inclusion entrapment can be lost to the shrinkage bubble during post-entrapment cooling. We show that the computational method of Riker (2005), which predicts the pre-eruption shrinkage bubble size as a function of the difference between trapping temperature and pre-eruption temperature, successfully reproduces our experimental results. Our results demonstrate that the mass of CO 2 contained in shrinkage bubbles must be considered to accurately infer original pressures of crystallization for melt inclusions. However, the effect is expected to be smaller for more H 2 O-rich melt inclusions than those studied here because the vapor bubble in such inclusions will have lower mole fractions of CO 2 than the low-H 2 O inclusions in our study.

The mafic magmatism of the last 50 ka on Terceira Island, Azores archipelago, occurred along three segments of the fissure zone that crosses the island. The two subaerial segments developed with different trends over pre-existing, quiescent or extinct, central volcanoes. The Serreta submarine ridge is the offshore segment of the fissure zone that erupted recently in 1998-2001. The combined study of CO 2 +H 2 O fluid inclusions hosted in mafic minerals and rock geochemistry of the magmas, reveals different storage and ascent conditions among the fissure zone segments. The maximum pressure of fluid trapping for all the fissure systems occurred at the Moho Transition Zone, between 498 and 575 MPa (20.3-21 km deep). At this depth interval all magmas stagnated for some time, before ascending toward the surface, experiencing fractional crystallization and degassing. Magmas of the southeastern and Serreta segments of the fissure zone ascended rapidly through the crust without further stops. Those of the central segment experienced a multi-step ascent, with fluid trapping at 406 and 209 MPa (16.5-8.5 km deep) and associated geochemical evolution toward trachybasalt. The magma ascent below the different segments of the fissure zone varies from almost isochoric at the submarine segment, associated with minimum re-equilibration of the inclusions, to polybaric slow ascent at the central segment, associated to almost complete re-equilibration of the inclusions. Variable degrees of re-equilibration and multi-step ascent may be linked to both the presence of preexisting intracrustal crystallized bodies of more evolved composition and the stress field acting on this area. The latter responds to the local and shallow conditions related to the presence of older central volcanoes and to the main regional spreading direction of the Terceira Rift, which at regional scale, is approximately orthogonal to the fissure zone axis.

Melt inclusions (MI) are considered the best tool available for determining the pre-eruptive volatile contents of magmas. H 2 O and CO 2 concentrations of the glass phase in MI are commonly used both as a barometer and to track magma degassing behavior during ascent due to the strong pressure dependence of H 2 O and CO 2 solubilities in silicate melts. The often unstated and sometimes overlooked requirement for this method to be valid is that the glass phase in the MI must represent the composition of the melt that was trapped at depth in the volcanic plumbing system. However, melt inclusions commonly contain a vapor bubble that formed after trapping owing to differential shrinkage of the melt compared to the host crystal, and/or crystallization at the inclusion-host interface. Such bubbles may contain a substantial portion of volatiles, such as CO 2 , that were originally dissolved in the melt. In this study, we determined the contribution of CO 2 in the vapor bubble to the overall CO 2 content of MI based on quantitative Raman analysis of the vapor bubbles in MI from the 1959 Kilauea Iki (Hawaii), 1960 Kapoho (Hawaii), 1974 Fuego volcano (Guatemala), and 1977 Seguam Island (Alaska) eruptions. We found that the bubbles typically contain 40 to 90% of the total CO 2 in the MI. Reconstructing the original CO 2 content by adding the CO 2 in the bubble back into the melt results in an increase in CO 2 concentration by as much as an order of magnitude (thousands of parts per million). Reconstructed CO 2 concentrations correspond to trapping pressures that are significantly greater than one would predict based on analysis of the volatiles in the glass alone. Trapping depths can be as much as 10 km deeper than estimates that ignore the CO 2 in the bubble. In addition to CO 2 in the vapor bubbles, many MI showed the presence of a carbonate mineral phase. Failure to recognize the carbonate during petrographic examination or analysis of the glass and to include its contained CO 2 when reconstructing the CO 2 content of the originally trapped melt will introduce additional errors into the calculated volatile budget. Our results emphasize that accurate determination of the pre-eruptive volatile content of melts based on analysis of melt inclusions must consider the volatiles contained in the bubble (and carbonates, if present). This can be accomplished either by analysis of the bubble and the glass followed by mass-balance reconstruction of the original volatile content of the melt, or by re-homogenization of the MI prior to conducting microanalysis of the quenched, glassy MI.

The Mars Science Laboratory (MSL) rover Curiosity has documented a section of fluvio-lacustrine strata at Yellowknife Bay (YKB), an embayment on the floor of Gale crater, approximately 500 m east of the Bradbury landing site. X‑ray diffraction (XRD) data and evolved gas analysis (EGA) data from the CheMin and SAM instruments show that two powdered mudstone samples (named John Klein and Cumberland) drilled from the Sheepbed member of this succession contain up to ~20 wt% clay minerals. A trioctahedral smectite, likely a ferrian saponite, is the only clay mineral phase detected in these samples. Smectites of the two samples exhibit different 001 spacing under the low partial pressures of H 2 O inside the CheMin instrument (relative humidity <1%). Smectite interlayers in John Klein collapsed sometime between clay mineral formation and the time of analysis to a basal spacing of 10 Å, but largely remain open in the Cumberland sample with a basal spacing of ~13.2 Å. Partial intercalation of Cumberland smectites by metal-hydroxyl groups, a common process in certain pedogenic and lacustrine settings on Earth, is our favored explanation for these differences. The relatively low abundances of olivine and enriched levels of magnetite in the Sheepbed mudstone, when compared with regional basalt compositions derived from orbital data, suggest that clay minerals formed with magnetite in situ via aqueous alteration of olivine. Mass-balance calculations are permissive of such a reaction. Moreover, the Sheepbed mudstone mineral assemblage is consistent with minimal inputs of detrital clay minerals from the crater walls and rim. Early diagenetic fabrics suggest clay mineral formation prior to lithification. Thermodynamic modeling indicates that the production of authigenic magnetite and saponite at surficial temperatures requires a moderate supply of oxidants, allowing circum-neutral pH. The kinetics of olivine alteration suggest the presence of fluids for thousands to hundreds of thousands of years. Mineralogical evidence of the persistence of benign aqueous conditions at YKB for extended periods indicates a potentially habitable environment where life could establish itself. Mediated oxidation of Fe 2+ in olivine to Fe 3+ in magnetite, and perhaps in smectites provided a potential energy source for organisms.

A method is developed for determining the diffusivity of infrared-active species by transmission Fourier transform infrared spectroscopy (FTIR) in samples prepared as rectangular prisms without cutting the sample. The primary application of this “whole-block” or “3D-WB” method is in measuring the diffusion of hydrogen (colloquially referred to as “water”) in nominally anhydrous minerals, but the approach is applicable to any IR-active species. The whole-block method requires developing a three-dimensional model that includes the integration of the beam signal through the sample, from rim to core to opposite rim. The analysis is carried out using both forward and tomographic inverse modeling techniques. Measurements collected from central slices cut from the whole block are simpler to interpret than whole-block measurements, but slicing requires destructive sample analysis. Because the whole-block method is nondestructive, this approach allows a time-series of diffusion experiments on the same sample. The potential pitfalls of evaluating whole-block measurements without correcting for path integration effects are explored using simulations. The simulations demonstrate that diffusivities determined from whole-block measurements without considering path-averaging may be up to half an order of magnitude too fast. The largest errors are in fast and/or short directions, in which the diffusion profiles are best developed. A key characteristic of whole-block measurements is that the central values in whole-block traverses always change before the concentration of the IR-active species changes in the block’s center because of signal integration that includes concentrations in the sample rims. The resulting plateau in the measurements is difficult to fit correctly without considering path integration effects, ideally by using 3D whole-block models. However, for early stages of diffusion with <50% progress, diffusivities can be accurately determined within 0.5 log units using a 1D approximation and the whole-block central plateau values because diffusivities are more dependent on profile shape than absolute concentrations. To test the whole-block method, a dehydration experiment was performed on an oriented piece of diopside from the Kunlun Mts with minimal zoning, cracks, or inclusions. The experiment was performed in a gas mixing furnace for 3 days at a temperature of 1000 °C and oxygen fugacity of 10-11.1 bar (QFM). First, whole-block analysis was performed by taking FTIR traverses in three orthogonal directions. Then, a slice was cut from the center of the sample, and hydrogen profiles were measured by FTIR and secondary ion mass spectrometry (SIMS). The results of FTIR and SIMS measurements on the slice are in good agreement both with each other and with diffusion profiles calculated based on the results of forward and inverse models of the whole-block FTIR measurements. Finally, the new method is applied to previous whole-block measurements of hydrogen diffusion in San Carlos olivine using both the forward and inverse approaches.

Here we apply the relatively new analytical technique of atom probe tomography (APT) to a naturally occurring isoferroplatinum grain (Pt 3 Fe) from northern California to constrain its origin and the nanoscale distribution of trace elements within the grain. Each analysis detected the positions of 10 million atoms in three dimensions with sub-nanometer spatial resolution. The (111) atomic planes are clearly resolved and their orientation was confirmed by electron backscatter diffraction (EBSD). The elemental concentrations of all elements (Pt, Fe, Ir, Ni, Rh, Ru, and Cu) determined from the APT mass/charge spectra are within 2 standard deviations of electron microprobe analysis (EMPA) of the grain. The isotopic abundances determined by APT matches NIST standard compositions over a wide range of concentrations, down to 100 ppmw. Nanoscale areas free of minor and trace elements are present throughout the sample. These could be due to the random distribution of atoms. Alternatively, the Pt-Fe phase diagram indicates that order-disorder precipitates of an L1 2 structure could have formed as the isoferroplatinum cooled from magmatic temperatures (Nose et al. 2003). The trace element free areas could be such precipitates, which would support a high-temperature igneous origin for the isoferroplatinum, rather than formation during low-temperature serpentinization. The results highlight the unique capabilities of APT and the potential utility of knowing the location and identity of atoms in nanometric volumes.

We studied V-shaped twins of chrysoberyl (BeAl 2 O4) from Rio das Pratinhas pegmatites near Arataca in the Bahia state of Brazil. The local structure of the twin boundaries was determined using powder X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) methods, and density functional theory (DFT) calculations. To provide the most reliable model for DFT and HRTEM simulations the structure of chrysoberyl was first refined in the orthorhombic space group 62 (Pmnb) with unit-cell parameters: a = 5.4825(1) Å, b = 9.4163(2) Å, and c = 4.4308(1) Å, with 0.5 at% of Fe 3+ present on the Al(2) sites, suggesting an average composition of BeAl 1.99 Fe 0.01 O 4 . TEM study of V-shaped twins showed that the twin boundary lies in the (130) planes, and the angle measured between the crystal domains related by mirror twin operation is ∼59.5°. Rigid structural model of (130) twin boundary in chrysoberyl was refined by DFT calculations, using a pseudo-potential method. The twin boundaries show local enrichment with Ti. Bulk chrysoberyl contains numerous nanosized TiO 2 precipitates with a distorted rutile structure, following the orientation relationship of [001] Ch {120} Ch ||[010] R {103} R . The increase of Ti at the twin boundaries and the formation of rutile-type TiO 2 precipitates in bulk chrysoberyl suggest a transient Ti-exsolution that took place after the twin formation.

Carbon speciation in and partitioning among silicate-saturated C-O-H fluids and (C-O-H)-saturated melts have been determined ∼1.7 GPa and 900 °C under reducing and oxidizing conditions. The measurements were conducted in situ while the samples were at the conditions of interest. The solution equilibria were (1) 2CH 4 + Q n = 2CH 3 − + H 2 O + Q n+1 and (2) 2CO 3 2- + H 2 O + 2Q n+1 = HCO 3 − + 2Q n , under reducing and oxidizing conditions, and where the superscript, n, in the Qn-species denotes number of bridging oxygen in the silicate species (Q-species). The abundance ratios, CH 3 /CH 4 and HCO 3 − /CO 3 2- , increase with temperature. The enthalpy change associated with the species transformation differs for fluids and melts and also for oxidized and reduced carbon [Reducing: ΔH(1) fluid = 16 ± 5 kJ/mol, ΔH(1) melt = 50 ± 5 kJ/mol; oxidizing ΔH(2) fluid = 81 ± 14 kJ/mol]. For the exchange equilibrium of CH 4 and CH 3 species between fluid and melt, the temperature-dependent equilibrium constant, (X CH₄ /X CH₃ )fluid/(X CH₄ / X CH₃ )melt, yields ΔH = 34 ± 3 kJ/mol. \ Increased abundance ratios, C H₄ /C H₃ and HCO 3 − /CO 3 2- , lead to increased polymerization of silicate+(C-O-H) melt. Because of such relations, melt transport properties (e.g., viscosity) and element partition coefficients between magmatic liquids, C-O-H fluids, and crystalline phases can vary by more than 100% with speciation changes of C-bearing volatiles upper mantle. These structure effects are more pronounced the higher the pressure and the more mafic the magma.

The multi-cycle heating and cooling thermogravimetric (TG) method was used to study the kinetic behavior of three kaolinite samples: defect-free Keokuk kaolinite, KGa-2 with a very low degree of structural order, and KGa-1 having intermediate structural order. In each cycle, the maximum cycle temperature (MCT) was set to 25 °C higher than the preceding cycle. The TG patterns consist of a set of subsequent DTG maxima representing the portions of OH groups that did not dehydroxylate in previous cycles. Each stage of partial dehydroxylation consists of two kinetic mechanisms and for each of them the experimental dα/dt values that characterize the reaction rate of the dehydroxylated fraction, α, within a period of the reaction time, t, were computed. One mechanism corresponds to a zero-order reaction that occurs in each cycle and indicates that the reaction is homogeneous and each non-dehydoxylated layer is transformed into metakaolinite layer without formation of intermediate derivatives. For this step of the cycles activation energy, Ea, was calculated from the linear relationship between ln(dα/ dt) and reciprocal temperature, T; for KGa-2 kaolinite, the E a varies from 32.0 to 38.1 kcal/mol; in KGa-1, Ea varies from 37.1 to 40.4 kcal/mol, whereas in Keokuk, E a varies from 42.7 to 47.5 kcal/ mol. The particular variation of the E a is discussed in terms of structural and morphological features of the samples. The kinetic mechanism of the second step of reaction corresponds to the temperature range higher than the first step of the same heating cycle. The second step starts from the point where α = α P that was found to vary between 0.25 and 0.45. The acceleration of the reaction rate of dehydroxylation within this interval decreases with increasing α and T, and the mechanism observed for each of the studied samples is independent of its stacking order, average particle size, and particle size distribution. The ƒ(α) is a function of the reaction mechanism in the second step and has the form ƒ(α) = (1 - α) n /(1 - n) where n is an empirical parameter and its value was found from <0.01 to 0.06-0.08 among cycles and samples. The value of n controls the reaction rate slowing or the deviation from the zero-order reaction and increases with increasing metakaolinite content. Using parameters n, α, and T determined for the second step, E a values were calculated for the second step of reaction in each heating cycle. For the Keokuk kaolinite, E a value varies from 31.6 to 37.5 kcal/mol, in KGa-1 Ea is 27.0-35.6 kcal/ mol, and in KGa-2 the E a value varies from 26.3 to 34.9 kcal/mol. A structural model explaining the acceleration rate slowing is discussed.

Zircon geochronology and geochemistry are increasingly important for understanding metamorphic processes, particularly at extreme conditions, but drivers of zircon dissolution and regrowth are poorly understood. Here, we model Zr mass balance to identify P-T regions where zircon should dissolve or grow. Zirconium contents of major metamorphic minerals were assessed from published data and new measurements, and models were constructed of mineralogical development and zircon abundance for hydrous MORB and metapelitic compositions along representative P-T paths. Excluding zircon, the minerals rutile, garnet, and hornblende strongly influence Zr mass balance in metabasites, accounting for as much as 40% of the whole-rock Zr budget. Clinopyroxene and garnet contain more Zr than plagioclase, so breakdown of plagioclase at the amphibolite to eclogite facies transition, should cause zircon to dissolve slightly, rather than grow. Growth of UHP zircon is predicted over a restricted region, and most zircon grows subsequently at much lower pressure. In metapelites, zircon is predicted to undergo only minor changes to modal abundance in solid state assemblages. Partial melting, however, drives massive zircon dissolution, whereas melt crystallization regrows zircon. From a mass-balance perspective, zircon growth cannot be attributed a priori to the prograde amphibolite-eclogite transition, to UHP metamorphism, or to partial melting. Instead, zircon should grow mainly during late-stage exhumation and cooling, particularly during oxide transitions from rutile to ilmenite and melt crystallization. As predicted, most zircons from HP/UHP eclogites of the Western Gneiss Region and Papua New Guinea substantially postdate eclogite formation and maximum pressures.

Following the characterization of the new amphibole species fluoro-leakeite, ideally A Na B Na 2 C (Mg 2 Al 2 Li) T Si 8 O 22 W F 2 , at Norra Kärr (Sweden), so far considered the type locality of eckermannite, re-examination of the holotype material of eckermannite deposited at the Museum of Natural History in London (BM 1949.151) and of the original sample analyzed by Törnebohm (1906) confirmed that they both are actually fluoro-leakeite. A survey of literature data showed that the only analysis reported for eckermannite is that of sample AMNH 108401 from the Jade Mine Tract, Myanmar. Complete characterization of that sample has led to the approval of a new holotype for eckermannite (IMA-CNMNC 2013-136), ideally A Na B Na 2 C (Mg 4 Al) T Si 8 O 22 W (OH) 2 , which is described in this work. Holotype eckermannite from Myanmar has the empirical unit formula A( Na 0.87 K 0.06 ) Σ=0.93 B (Na 1.89 Ca 0.11 ) Σ=2.00 C (Mg 3.87 Fe 2+ 0.09 Mn 0.01 Fe 3+ 0.38 Al 0.62 ) Σ=4.97 T Si 8.00 O 22 W (F 0.03 OH 1.97 ) Σ=2.00 . It is monoclinic, C2/m, with a = 9.8087(7), b = 17.8448(13), c = 5.2905(4) Å, β = 103.660(1), V = 899.8(1) Å 3 ; Z = 2, D calc = 3.02 g/cm 3 . Optics: biaxial (-); α = 1.605, β = 1.630, γ = 1.634 all ±0.002 (λ = 590 nm). The 10 strongest reflections in the X‑ray powder pattern [d values (in Å), I, (hkl)] are: 2.702, 100, [(3̄31) (151)]; 3.395, 59, (131); 3.128, 56, (310); 2.525, 56, (2̄02); 8.407, 42, (110); 2.574, 36, [(061) (002)]; 3.257, 34, (240); 2.161, 33, (261); 2.966, 33, (060); 4.460, 30, (040). The reason for the rarity of eckermannite compositions are examined and discussed based on considerations on the short-range order of A cations and W anions.

Finely acicular rutile intergrown with host quartz (rutilated quartz) is commonly found in hydrothermal veins, including the renown cleft mineral locations of the Swiss Alps. These Alpine cleft mineralizations reportedly formed between ∼13.5 and 15.2 Ma (based on ages of rare hydrothermal monazite and titanite) at temperatures (T) of ∼150-450 °C (based on fluid inclusions and bulk quartz-mineral oxygen isotope exchange equilibria), and pressures (P) of 0.5-2.5 kbar (estimated from a geothermal gradient of 30 °C/km). The potential of rutilated quartz as a thermochronometer, however, has not been harnessed previously. Here, we present the first results of age and T determinations for rutilated quartz from six locations in the Swiss Alps with vein country rocks that cover peak-metamorphic conditions between ∼600 and <350 °C. Samples were cut and mounted in epoxy disks to expose rutile (∼30 to 1400 μm in diameter) and its host quartz. Cathodoluminescence (CL) and backscattered electron (BSE) imaging of host quartz and rutile inclusions, respectively, shows internal zonations, which are nevertheless isotopically homogeneous. Newly developed secondary ionization mass spectrometry (SIMS) oxygen isotopic analysis protocols for rutile were combined with those established for trace elements (including Zr) and U-Pb ages in rutile, and Ti abundances in the host quartz. U-Pb rutile ages average 15.1 ± 1.7 Ma (2σ), in excellent agreement with previous accessory mineral geochronometers. Pressure-independent T estimates, calibrated for low-temperature conditions, from oxygen isotope fractionation between rutile and quartz in touching pairs are 310-576 °C. Individual rutile needles vary in Zr abundances beyond analytical uncertainties, but average Zr-in-rutile inversely correlates with oxygen isotopic fractionation between quartz and rutile. Linear regression of the data yields: with x = Zr ppm and R = 0.008314 (uncertainties scaled by the square root of the mean square of weighted deviates MSWD = 11; n = 9). This relationship supports previously recognized temperaturedependent Zr uptake in rutile, although widely used Zr-in-rutile thermometer calibrations based on high-T experiments are at variance with oxygen isotope exchange temperatures. By contrast, Ti-inquartz lacks systematic relations with oxygen isotope temperatures. The discrepancy between low-T Ti-in-quartz thermometry on one side, and oxygen isotope and Zr-in-rutile thermometry on the other, suggests that Ti-in-quartz thermometry should be applied with caution for low-T (<500 °C) rocks.

Nickel is typically distributed across several fine-grained minerals in nickel laterites, formed by intense tropical weathering of ultramafic rocks. Indonesia accounts for approximately 16% of the world’s lateritic nickel reserves, which play an increasing role in global nickel production. However, relatively few geochemical studies of Indonesian laterites have been undertaken and quantification of Ni speciation is unclear. In this study the Ni geochemistry of an Indonesian laterite composed of limonite and saprolite has been examined using synchrotron microprobe analysis (microprobe X-ray fluorescence microscopy, μ-XFM; microprobe X-ray diffraction, μ-XRD; microprobe X-ray absorption spectroscopy; μ-XAS) and bulk XAS. This approach provides semi-quantitative species specific information not readily obtainable using traditional laboratory methods that are hampered by the fine-grained heterogeneous nature of laterites. In the limonite 16 ± 4% of the Ni was found to be substituted for Al in lithiophorite with 26 ± 7% being associated with lizardite (a serpentine) substituted for Mg. A minor proportion of the Ni is adsorbed onto the Mn layers of phyllomanganate (e.g., lithiophorite). However the majority of the Ni, 58 ± 15% is substituted for Fe in goethite. The majority of the Ni (85 ± 21%) within the saprolite is found to be associated with lizardite, the predominant mineral. A few relatively large Ni asbolane grains are also observed, which account for 14 ± 3% of the Ni with the remaining 1 ± 0.3% of the Ni replacing Fe within goethite.

In the present study, we computed the thermo-chemical and thermo-physical properties of the 2M 1 polytype of muscovite in the 0-10 GPa and 0-900 K ranges, using the hybrid DFT/B3LYP-D* density functional, corrected to take into account dispersive forces, and by using the quasi-harmonic approximation. The bulk modulus K T0 of muscovite, its first derivative K′, and the unit-cell volume at zero pressure V 0 at 298.15 K, calculated using a third-order Birch-Murnaghan equation of state, were K T0 = 59.93 GPa, K′ = 7.84, and V 0 = 940.6 Å 3 . Our theoretical data are in good agreement with previous experimental results obtained by X‑ray diffraction. Thermal bulk moduli, K T , thermal expansion coefficients, α T , and heat capacity at different P-T conditions are given, which could be useful in both geophysical and technological applications. The results of this kind of analysis can be used in the study of the thermodynamic properties of solid phases at physical conditions that are difficult to obtain during experimental procedures, especially under controlled high pressures and temperatures.

Previous studies of hydrous glasses and melts with infrared spectroscopy have led to the conclusion that the IR combination peaks near 4500 and 5200 cm -1 reflect the existence of OH- (hydroxyl) groups and H 2 O mol water molecules in those materials. Here, we show that the glass chemical composition can impact profoundly the intensities and frequencies of the fundamental O-H stretching signal and, therefore, potentially those of the 4500 and 5200 cm -1 combination peaks. In alkali silicate glasses, compositional effects can give rise to peaks assigned to fundamental O-H stretching at frequencies as low as 2300 cm -1 . This expanded range of Raman intensity assigned to O-H stretch is increasingly important as the ionic radius of the alkali metal increases. As a result, the combination of the fundamental O-H stretch in OH - groups with the Si-O-H stretch located near 910 cm -1 gives rise to a complex combination signal that can extend to frequencies much lower than 4200 cm -1 . This combination signal then becomes unresolvable from the high-frequency limb of the band assigned to fundamental O-H stretch vibration in the infrared spectra. It follows that, when O-H stretch signals from OH- groups extend to below 3000 cm -1 , the 4500 cm -1 peak does not represent the total OH - signal. Under such circumstances, this infrared peak may not be a good proxy for determining the concentration of OH - hydroxyl groups for glassy silicate materials.

Monazite and zircon thermometry and geochronology were applied to anatectic pelites of the northern East Humboldt Range, Nevada. The study area is an exhumed portion of the Sevier orogenic root and is characterized by two crustal blocks with different prograde metamorphic histories: the Winchell Lake nappe and the underlying Lizzies Basin block. U/Th-Pb secondary ion mass spectrometry (SHRIMP) results from zircon and monazite indicate that in the Lizzies Basin block prograde metamorphism began by 96.5 ± 8.0 Ma. Cooling and melt crystallization was initiated by 80.1 ± 1.4 Ma. Possible reheating and a monazite growth event occurred again at 76.2 ± 2.8 to 68.2 ± 2.0 Ma. In the upper limb of the overlying Winchell Lake nappe, prograde metamorphism began by 82.8 ± 1.3 Ma. Cooling and melt crystallization recorded by zircon and monazite growth/recrystallization at 77.4 ± 12.4 to 58.9 ± 3.6 Ma. Melt may have been present in the Winchell Lake nappe upper limb for a protracted period, or may have formed during several unresolved melting events. Thin Eocene-Oligocene (~40-32 Ma) high-Y monazite rims are found in both crustal blocks. These probably represent a phase of heating during Eocene-Oligocene magmatism and extensional deformation. U/Th-Pb geochronology results are consistent with differential burial, heating, and exhumation of different crustal blocks within the East Humboldt Range. Significantly fast exhumation of upper limb rocks of the Winchell Lake nappe and somewhat slower exhumation of Lizzies Basin block rock occurred prior to the “core complex” phase of the exhumation of the Ruby Mountains-East Humboldt Range metamorphic core complex. Differences in the timing and tectonic significance of exhumation episodes within the East Humboldt Range may reflect how the localized presence of partial melt can affect the evolution of an exhumed orogenic terrane.

Mineralogical measurements from spectral remote sensing and remote geochemical measurements from gamma-ray and neutron spectrometers are complementary data sets that have been used together successfully to study the distributions of iron, titanium, and rare earth elements on the Moon. We compare neutron and gamma-ray data sets from Lunar Prospector and find them in good agreement with each other within the errors of previously developed equations that relate neutron flux with geochemistry, but find small adjustments to the nominal values are warranted. We used the neutron-validated LP GRS oxides to improve Clementine-based global mineral maps. The comparison was enabled by converting the minerals of Lucey (2004) to oxides using stoichiometry and assumptions about Mg#, calcium content of clinopyroxenes, and An#. We find that FeO and Al 2 O 3 derived from the maps of Lucey (2004) do not follow the expected negative correlation seen in lunar samples, but can be brought into agreement with samples and with LP GRS oxides by increasing plagioclase in proportion with orthopyroxene abundance, while simultaneously decreasing Mg#. We interpreted this to mean that plagioclase and orthopyroxene exist in rocks together (as in a noritic rock) with the spectrally difficult to detect plagioclase being masked by the strong spectral signature of the orthopyroxene. We generated a revised set of maps of the major lunar minerals and a map of Mg# for the mafic minerals that are consistent with Lunar Prospector neutron and gamma-ray spectrometer results and show greatly improved agreement with lunar soil samples over previous global mineral maps from Clementine.

The presence of anorthosite in the lunar highlands containing plagioclase that is compositionally less calcic than plagioclase in the ferroan anorthosites cannot be readily explained by the current lunar paradigm in which lunar anorthosite was produced as a floatation cumulate in the lunar magma ocean. Phase-equilibrium experiments were conducted to investigate whether such anorthosite could arise locally from crystallization of aluminous magma at shallow levels within the lunar crust. The experiments were conducted on a synthetic analog of Cl-, F-, and S-bearing aluminous highland basalt 14053 at pressures of approximately 1 bar and ƒ O₂ at ~QIF. Pyroxene and plagioclase (An 93-89 ) saturation occurs early, and with continued crystallization, the residual liquid evolves to a silica-poor, halogen-, Fe-, and Ti-rich melt with a computed density of >3.1 g/mL. This liquid remains higher in density than the plagioclase over the crystallization interval, providing the possibility of plagioclase/ melt separation by liquid draining. A model is proposed in which “alkali” anorthosite, consisting of sodic anorthite or bytownite, coupled with underlying pyroxenite (or harzburgite) is produced locally during crystallization of plagioclase from “Al-rich” magmas at or within roughly a kilometer of the lunar surface. In this model, segregation of plagioclase would be attained by settling of ferromagnesian minerals to the bottom of a shallow magma chamber, and draining of low-viscosity, low-silica, Fe-Ti-K-REE-P-enriched residual basaltic melt to deeper regions of the crust, or into topographic lows. Such residual melt may be represented by magma compositions similar to some of the intermediate- to high-Ti mare basalts. This model would provide a mechanism that can account for the more “alkali” anorthosite identified in widespread isolated locales on the Moon and allow for variable ages for such anorthosite that may extend to ages of the mare basalts.

The exposure of mantle peridotite to water at crustal levels leads to a cascade of interconnected dissolution-precipitation and reduction-oxidation reactions-a process referred to as serpentinization. These reactions have major implications for microbial life through the provision of hydrogen (H 2 ). To simulate incipient serpentinization under well-constrained conditions, we reacted centimeter-sized pieces of uncrushed harzburgite with chemically modified seawater at 300 °C and 35 MPa for ca. 1.5 yr (13 441 h), monitored changes in fluid chemistry over time, and examined the secondary mineralogy at the termination of the experiment. Approximately 4 mol% of the protolith underwent alteration forming serpentine, accessory magnetite, chlorite, and traces of calcite and heazlewoodite. Alteration textures bear remarkable similarities to those found in partially serpentinized abyssal peridotites. Neither brucite nor talc precipitated during the experiment. Given that the starting material contained ~4 times more olivine than orthopyroxene on a molar basis, mass balance requires that dissolution of orthopyroxene was significantly faster than dissolution of olivine. Coupled mass transfer of dissolved Si, Mg, and H + between olivine and orthopyroxene reaction fronts was driven by steep activity gradients and facilitated the precipitation of serpentine. Hydrogen was released in significant amounts throughout the entire experiment; however, the H 2 release rate decreased with time. Serpentinization consumed water but did not release significant amounts of dissolved species (other than H 2 ) suggesting that incipient hydration reactions involved a volume increase of ~40%. The reduced access of water to fresh olivine surfaces due to filling of fractures and coating of primary minerals with alteration products led to decreased rates of serpentinization and H 2 release. While this concept might seem at odds with completely serpentinized seafloor peridotites, reaction-driven fracturing offers an intriguing solution to the seemingly self-limiting nature of serpentinization. Indeed, the reacted sample revealed several textural features diagnostic of incipient reaction-driven fracturing. We conclude that fracturing must have far reaching impacts on the rates of serpentinization and H 2 release in peridotite-hosted hydrothermal systems.

Inhalation of erionite has been proven to be the cause of the extended epidemic of malignant mesothelioma occurring in Central Anatolia, Turkey, and of cases of lung diseases in the U.S.A. Its carcinogenicity is three orders of magnitude greater than that of regulated asbestos. Here we report the results of the investigation of the structural and crystal chemical modifications occurring in erionite leached with artificial lysosomal fluid (ALF) and Gamble’s solution. ALF leaching produces a migration of Na + ions from Ca1 to Ca2 extraframework cationic site, without the occurrence of any significant modification of the chemical composition of the fibers. In contrast, leaching with Gamble’s solution induces a complex ionic-exchange process resulting in a temporary partial replacement of Na + by Ca 2+ , coming from the fluid, which is fixed at a third Ca3 cationic site. Subsequently, the exchange process reverses. In fact, Ca 2+ is removed from Ca3 and Na + migrates back to Ca1, the structure being indistinguishable from the starting, unleached material. Such processes seem to be accompanied by a progressive amorphization of fibers. Present data could provide valuable background for a more detailed comprehension of the morphostructural/biological activity relationships inducing pathogenicity.

The understanding of redox equilibria as well as the knowledge of the elemental distribution in magmatic melts are of fundamental importance to constrain the genesis of magmas. In particular, the partitioning of trace elements (e.g., Eu) has demonstrated to be a useful tool for estimating the redox conditions in Earth and planetary materials. However, for a more complete comprehension of Eu in silicate melts, information regarding the effects of temperature (T), redox conditions, compositions, and the possible interference of other multivalent elements is still lacking. Here we provide new data on the oxidation states of two commonly coexistent multivalent elements (Eu and Fe) in melts, acquired by “in situ” dispersive X-ray absorption spectroscopy experiments at high temperatures and at different oxygen fugacity conditions. This work, for the first time, shows the possibility to monitor in real-time the behavior and valence variations of two elements under varying environmental conditions (like T and redox state).