Published by De Gruyter

Volume 96 Issue 7

Issue of American Mineralogist

Contents
Journal Overview

April 2, 2015

Needs and opportunities in mineral evolution research

Robert M. Hazen, Andrey Bekker, David L. Bish, Wouter Bleeker, Robert T. Downs, James Farquhar, John M. Ferry, Edward S. Grew, Andrew H. Knoll, Dominic Papineau, Jolyon P. Ralph, Dimitri A. Sverjensky, John W. Valley

Page range: 953-963

Abstract

Progress in understanding mineral evolution, Earth’s changing near-surface mineralogy through time, depends on the availability of detailed information on mineral localities of known ages and geologic settings. A comprehensive database including this information, employing the mindat.org web site as a platform, is now being implemented. This resource will incorporate software to correlate a range of mineral occurrences and properties vs. time, and it will thus facilitate studies of the changing diversity, distribution, associations, and characteristics of individual minerals as well as mineral groups. The Mineral Evolution Database thus holds the prospect of revealing mineralogical records of important geophysical, geochemical, and biological events in Earth history.

April 2, 2015

Rutile inclusions in quartz crystals record decreasing temperature and pressure during the exhumation of the Su-Lu UHP metamorphic belt in Donghai, East China

Xiaofeng Li, Brian Rusk, Rucheng Wang, Yuichi Morishita, Yasushi Watanabe, Zhenyu Chen

Page range: 964-973

Abstract

Donghai County in the Jiangsu Province of East China is known for its large-scale production of high-quality quartz crystals. The quartz crystals are hosted within the Su-Lu ultrahigh-pressure (UHP) metamorphic belt. They form in quartz veins hosted by eclogite and gneiss, or along contacts between eclogite and gneiss and are mined as placer deposits in the Quaternary sediments. Backscattered electron imaging of the rutile in rutile-bearing euhedral quartz crystals from this region reveal three compositionally and texturally distinct generations of rutile, encapsulated within the host quartz crystal. The earliest generation of rutile (R1) is brightest in BSE, reflecting enrichment in Fe 2 O 3 (0.75-2.08 wt%), Nb 2 O 5 (0.37-0.93 wt%), WO 3 (0.48-2.99 wt%), and ZrO 2 (0.005-0.105 wt%), relative to R2 and R3. R2 rutile overgrows R1 rutile and contains 0.66-1.11 wt% Fe 2 O 3 , 0.45-0.74 wt% Nb 2 O 5 , 0.09-0.20 wt% WO 3 , and <0.001-0.013 wt% ZrO 2 . R3 rutile, which is the only rutile generation in contact with the host quartz crystals is darkest in BSE and always overgrows R1 and rounded aggregates of R2. R3 rutile contains 0.40-0.68 wt% Fe 2 O 3 , 0.13-0.37 wt% Nb 2 O 5 , 0.03-0.12 wt% WO 3 , and <0.001 wt% ZrO 2 . Oxygen isotopes decrease progressively from 0.6 to -1.5‰ in R1 rutile to 0.1‰ in R2 rutile to -5.1 to -0.3‰ in R3 rutile, consistent with decreasing temperature of rutile crystallization. Combined application of the Zr in rutile and Ti in quartz thermobarometers indicate that these rutile generations precipitated at progressively lower pressures and temperatures, consistent with previously determined retrograde metamorphic conditions of the Su-Lu UHP belt. R1 grew after peak metamorphism during retrograde eclogite facies metamorphism at temperatures between 720 and 800 °C and pressures between 21.7 and 26.6 kbar. During subsequent retrograde metamorphism, R1 was fractured and partially brecciated and overgrown by R2 during epidote-amphibolite facies retrograde metamorphism in the range of 400 to 500 °C and 5 kbar. Zirconium concentrations of <14 ppm in R3 rutile and Ti concentrations of <1 ppm in the co-precipitated host quartz suggest that they both grew at low temperatures of <300° and pressures <2 kbars. Oscillatory growth zones in quartz revealed by cathodoluminescence suggest that no subsequent metamorphism or hydrothermal activity occurred after the formation of the host euhedral quartz crystals and is consistent with a low temperature of quartz crystallization. The random distribution of rutile crystals in the quartz and the lack of evidence for rutile transport by hydrothermal fluids indicate that the host quartz formed by a dissolution-replacement process, whereby the original host mineral, likely omphacite or garnet, was replaced by quartz, but the rutile was not significantly replaced or dissolved due to the low solubility of Ti in low-temperature hydrothermal fluids.

April 2, 2015

A first-principles study of the phase transition from Holl-I to Holl-II in the composition KAlSi₃O₈

Liwei Deng, Xi Liu, Hong Liu, Yigang Zhang

Page range: 974-982

Abstract

The phase relation and structural evolution of Holl-I and Holl-II in the composition KAlSi 3 O 8 at 0 K have been investigated by the first-principles method up to 130 GPa. Holl-I and Holl-II are polymorphs of KAlSi 3 O 8 stable at low pressures and high pressures, respectively. The transition pressure is determined at -23(5) GPa, in agreement with recent experimental observations. All experimentally observed major changes associated with this phase transition such as the deviation of the γ-angle from 90°, splitting of the a- and b-axes, as well as its P-V evolution, are successfully simulated. By evaluating the effect of different Al/Si substitution mechanisms on the computing cell of Holl-I, we have found: (1) different Al/Si substitution mechanisms do not result in apparent difference in the minimized cohesive energies, suggesting a possible random distribution of Al and Si; (2) different Al/ Si substitution mechanisms lead to different powder X‑ray diffraction features, which, compared to the experimentally observed powder X‑ray diffraction data, implies that local non-random distribution of Al and Si exists to some extent in the Holl-I structure; and (3) the phase transition from Holl-I to Holl-II might be associated with a change in the distribution pattern of Al and Si in the structure. From the simulated compression data, we have derived K 0 = 174 GPa and V 0 = 244.82 Å 3 for Holl-I, and K 0 = 168 GPa and V 0 = 244.8 Å 3 for Holl-II (K 0 ′ fixed at 4). The larger K 0 of Holl-I is probably related to the more stable squared open tunnel delimited by the rigid tetragonal octahedral framework, which is gradually deformed by compression in Holl-II after the phase transition from Holl-I to Holl-II.

April 2, 2015

Sejkoraite-(Y), a new member of the zippeite group containing trivalent cations from Jáchymov (St. Joachimsthal), Czech Republic: Description and crystal structure refinement

Jakub Plášil, Michal Dušek, Milan Novák, Jiří Čejka, Ivana Císařová, Radek Škoda

Page range: 983-991

Abstract

Sejkoraite-(Y), the triclinic (Y 1.98 Dy 0.24 ) Σ2.22 H + 0.34 [(UO 2 ) 8 O 88 O 7 OH(SO 4 ) 4 ](OH)(H 2 O) 26 , is a new member of the zippeite group from the Červená vein, Jáchymov (Street Joachimsthal) ore district, Western Bohemia, Czech Republic. It grows on altered surface of relics of primary minerals: uraninite, chalcopyrite, and tennantite, and is associated with pseudojohannite, rabejacite, uranopilite, zippeite, and gypsum. Sejkoraite-(Y) forms crystalline aggregates consisting of yellow-orange to orange crystals, rarely up to 1 mm in diameter. The crystals have a strong vitreous luster and a pale yellow-to-yellow streak. The crystals are very brittle with perfect {100} cleavage and uneven fracture. The Mohs hardness is about 2. The mineral is not fluorescent either in short- or long-wavelength UV radiation. Sejkoraite-(Y) is yellow, with no visible pleochroism, biaxial negative with α′ = 1.62(2), β′ = 1.662(3), γ′ = 1.73(1), 2V calc = 79°. The empirical chemical formula (mean of 8 electron microprobe point analyses) was calculated on the basis of 12 (S + U) atoms: (Y 1.49 Dy 0.17 Gd 0.11 Er 0.07 Yb 0.05 Sm 0.02 ) Σ1.90 H + 0.54 [(UO 2 ) 8.19 O 7 OH(SO 4 ) 3.81 ](H 2 O) 26.00 . Sejkoraite-(Y) is triclinic, space group P1̄, a = 14.0743(6), b = 17.4174(7), c = 17.7062(8) Å, α = 75.933(4), β = 128.001(5), γ = 74.419(4)°, V = 2777.00(19) Å 3 , Z = 2, D calc = 4.04 g/cm 3 . The seven strongest reflections in the X-ray powder diffraction pattern are [dobs in Å (I) (hkl)]: 9.28 (100) (100), 4.64 (39) (200), 3.631 (6) (1̄42), 3.451 (13) (1̄44), 3.385 (10) (2̅4̅2), 3.292 (9) (044), 3.904(7) (300), 2.984 (10) (1̄4̅2). The crystal structure of sejkoraite-(Y) has been solved by the charge flipping method from single-crystal X-ray diffraction data and refined to R obs = 0.060 with GOF obs = 2.38, based on 6511 observed reflections. The crystal structure consists of uranyl sulfate sheets of zippeite anion topology, which alternate with an interlayer containing Y 3+ (H 2 O)n polyhedra and uncoordinated H 2 O groups. Two yttrium atoms are linked to the sheet directly via uranyl oxygen atom, and the remaining one is bonded by hydrogen bonds only. In the Raman and infrared spectrum of sejkoraite-(Y) there are dominating stretching vibrations of SO 4 tetrahedra (-1200-1100 cm -1 ), UO 2 2+ stretching vibrations (-900-800 cm -1 ), and O-H stretching (-3500-3200 cm -1 ) and H-O-H bending modes (-1640 cm -1 ). The new mineral is named to honor Jiří Sejkora, a Czech mineralogist of the National Museum in Prague.

April 2, 2015

Thermoelastic and thermodynamic properties of plagioclase feldspars from thermal expansion measurements

Mario Tribaudino, Marco Bruno, Fabrizio Nestola, Daria Pasqual, Ross J. Angel

Page range: 992-1002

Abstract

Powder X‑ray diffraction patterns between 90 and 935 K have been collected for nine plagioclase samples, with different compositions and degree of Al-Si order. The refined volumes have been modeled using the Wallace and Suzuki formulations based on the Mie-Grüneisen EOS. No significant difference has been found between the Suzuki and Wallace formulations, and between the Einstein and Debye approximations of lattice energy. A Wallace model with the first derivative of the bulk modulus constrained to the experimentally determined values leads to refined Grüneisen parameters between 0.49 and 0.41, without any definite trend between albite and anorthite; the Einstein temperature in intermediate plagioclase is θ E - 650 K, but it is lower in albite [θ E = 453(5) K]. A good fit with experimental heat capacity data for the An60Ab40 composition has been found using two Einstein-like oscillators with θ E1 = 230(3) K and θ E2 = 952(7) K, X θE1 = 0.391(5). The change with temperature in An 60 Ab 40 of the Grüneisen parameter is small at T > 150 K, with a slight decrease with temperature. Similar results could be obtained by independent refinement of an Einstein model with two oscillators to the volume data for the same composition [θ E1 = 205(30) K, θ E2 = 873(52) K, and X = 0.36(4)]. The components of the thermal strain tensor with temperature have been calculated and confirm that the greatest deformation is along the a* axis, i.e., along the extension direction of the crankshaft chains of the feldspar structure. Anomalous behavior of the strain tensor components in the a-c plane has been observed in albite and An 27 Ab 73 , and is related to an increase in the c unit-cell parameter with decreasing temperature.

April 2, 2015

Quantitative determination of chrysotile in massive serpentinites using DTA: Implications for asbestos determinations

C. Viti, C. Giacobbe, A.F. Gualtieri

Page range: 1003-1011

Abstract

There is increasing concern about the health hazard of asbestos from natural geologic deposits such as greenstones [natural occurring asbestos (NOA)]. Therefore, quantitative determination of the chrysotile asbestos content within massive serpentinites is a recurrent requirement of recent asbestos-inherent law regulations, due to the possible health hazard associated with the release of chrysotile fibers. Unfortunately, the obtainment of accurate and precise quantitative figures of the actual chrysotile content is strongly complicated by typical serpentinite textures, consisting of fineto- ultrafine intergrowths of fibrous and non-fibrous serpentine minerals, often difficult to identify by conventional methods, such as X-ray diffraction or microanalytical approaches. In this paper, we propose a reliable and straightforward method for the quantitative determination of chrysotile asbestos within bulk massive serpentinites, based on thermal analysis data and, specifically, on the distinctive thermal behavior of chrysotile, lizardite, and antigorite during dehydroxylation at 500-800 °C. Deconvolution processing of DTA endothermic signals in the dehydroxylation temperature range revealed good linear correlation between peak area ratios and chrysotile content, for both lizardite + chrysotile and antigorite + chrysotile samples. The DTA correlation curves have been used to determine the chrysotile content in two test serpentinites, revealing surprisingly high-chrysotile content. This novel method is of vast importance as it represents one of the most promising tools for chrysotile quantitative determinations in massive serpentinites, providing unbiased and accurate responses to recent asbestos-related law requirements.

April 2, 2015

In situ observation of the crystallization pressure induced by halite crystal growth in a microfluidic channel

Kotaro Sekine, Atsushi Okamoto, Kazuo Hayashi

Page range: 1012-1019

Abstract

Halite crystal growth was conducted within a polydimethylsiloxane (PDMS) microfluidic device to understand the mineral deposition behavior in a confined environment as well as the properties and evolution of the crystallization pressure. Supersaturation was induced by cooling a NaCl solution from 35 to 25 °C, and time-lapse images of halite crystal growth in the PDMS channel were collected. Halite crystal growth caused the PDMS to deform when the crystal faces reached the PDMS channel walls. The interface between the halite crystal and the channel wall changed over time and showed non-equilibrium behavior. Deformation of the PDMS wall was evident from the photoelastic effect within the PDMS material. The crystallization pressure in the laboratory experiments was quantitatively evaluated through numerical models of microscopic PDMS deformation due to halite crystal growth. Halite indentation observed in the laboratory experiments was reproduced in the model based on the retardance observed by the photoelastic effects of the PDMS. The crystallization pressure, defined as the normal stress acting to the PDMS wall surface from the halite crystal, was inhomogeneously distributed along the interface, with a maximum value of 2.0 MPa at the crystal corner. PDMS microfluidic devices are useful for understanding the behavior of mineral precipitation in confined environments. Deformation analysis of the photoelastic stress, along with numerical modeling, may be used to examine the nature of the crystallization pressure and to shed light on the mechanism of deformation due to the crystallization pressure.

April 2, 2015

Microstructures of the larval shell of a pearl oyster, Pinctada fucata, investigated by FIB-TEM technique

Naoki Yokoo, Michio Suzuki, Kazuko Saruwatari, Hideo Aoki, Katsuaki Watanabe, Hiromichi Nagasawa, Toshihiro Kogure

Page range: 1020-1027

Abstract

The structure of the larval shell of a pearl oyster, Pinctada fucata, has been investigated at several growing stages mainly using the focused ion beam (FIB) sample preparation technique and transmission electron microscopy (TEM). Until 12 h from fertilization, the larva does not have any calcified shells. After 18 h from fertilization, the embryo is covered with the first shell made of aragonite with the c-axis normal to the shell. The cross-sectional view of the shell shows a columnar contrast, but plan-view observation revealed that the columnar contrast does not correspond to individual crystals but is related to dense polycyclic {110} twins in the aragonite crystal. After 48 h from fertilization, the larvae formed a new aragonite layer under the initial layer; a homogeneous layer with globular contrast. The c-axis of the globules is normal to the shell. The orientation of the other axes is aligned locally but random in general. Additionally, larvae consisting of monolithic calcite as the inner layer were found at this stage. One to three weeks from fertilization, a new aragonite layer with a prismatic contrast is formed under the homogeneous layer. This layer consists of prismatic grains of aragonite, with their c-axes parallel to the prisms. High-angle annular dark-field (HAADF) images suggest that a considerable amount of organic molecules may be contained in the homogeneous layer but not in the inner prismatic layer, implying that the texture of each layer is related to the amount of organic molecules incorporated.

April 2, 2015

Magnesium quantification in calcites [(Ca,Mg)CO₃] by Rietveld-based XRD analysis: Revisiting a well-established method

Jürgen Titschack, Friedlinde Goetz-Neunhoeffer, Jürgen Neubauer

Page range: 1028-1038

Abstract

Mg-calcites commonly occur in natural environments, with Mg-contents ranging between about 0 and 32 mol% (referring to MgCO 3 ). Often, different Mg-calcite phases occur within the same sample. The Mg-content in calcites permits the classification of the diagenetic environment (marine vs. meteoric), or the reconstruction of paleotemperatures from skeletal remains. Since the 1960s, there have been published various calibrations for Mg determination in calcites based on XRD measurements. Recently, this method has come to be superseded by wet chemical, laser ablation, and microprobe analysis, due to their higher accuracy and/or higher sample resolution of these latter methods. This study presents a new calibration for the Mg determination in calcites using XRD measurements analyzed by means of the Rietveld refinement method. The calibration is based on lattice parameters and exhibits a reliable Mg-determination accuracy of more than 0.8 mol% between 0 and 15.5 mol%. The incorporation of the calibration into the Rietveld refinement software TOPAS permits a fast, standardized workflow. This, in turn, enhances the user-friendliness and the reproducibility of results, as well as allows the simultaneous analysis of multiple Mg-calcites in a sample. Mixtures of two Mg-calcites were analyzed using this new method. The Mg-content of two co-occurring Mg-calcite phases can be reliably quantified providing the Mg-calcites differ by at least 4.9 mol% and the minor Mg-calcite phase makes up more than 2.7 wt%. If the Mg-calcite phases differ by 3.4 mol% or less, the reliable identification of different Mg-calcite phases is questionable, due to the fact that differences involved here are too small. If such XRD patterns are refined with only one Mg-calcite phase, then the systematic misfit between measured and refined pattern can be used for the identification of a second Mg-calcite phase down to a difference in the Mg-content of about 3 mol%. However, a reliable phase quantification for these patterns cannot be achieved.

April 2, 2015

The effect of Fe on olivine H₂O storage capacity: Consequences for H₂O in the martian mantle

A.C. Withers, M.M. Hirschmann, T.J. Tenner

Page range: 1039-1053

Abstract

To investigate the influence of chemical composition on the behavior of H 2 O in Fe-rich nominally anhydrous minerals, and to determine the difference between H 2 O behavior in the martian and terrestrial mantles, we conducted high-pressure H 2 O storage capacity experiments employing a wide range of olivine compositions. Experiments were conducted with bulk compositions in the system FeO-MgO-SiO 2 -H 2 O with Mg no. [Mg no. = 100 × molar Mg/(Mg+Fe)] ranging between 50 and 100 at 3 GPa in a piston-cylinder and at 6 GPa in a multi-anvil apparatus. Experiments at 3 GPa were conducted at 1200 °C, with f O₂ buffered by the coexistence of Fe and FeO, and at 1300-1500 °C in unbuffered assemblies. Experiments at 6 GPa were conducted at 1200 °C without buffers. Experiments at 1200 °C produced olivine+orthopyroxene+hydrous liquid (liq), and higher T experiments produced olivine+liq. Additionally, we synthesized a suite of 7 olivine standards (Mg no. = 90) for low blank secondary ion mass spectrometry (SIMS) analysis of H in multi-anvil experiments at 3-10 GPa and 1250 °C, resulting in large (200-400 μm) homogeneous crystals with 0.037 to 0.30 wt% H 2 O. Polarized Fourier transform infrared (FTIR) measurements on randomly oriented grains from the synthesis experiments were used to determine principal axis spectra through least-squares regression, and H contents were calculated from the total absorbance in the OH stretching region. Using these olivines as calibrants for SIMS analyses, the H contents of olivines and pyroxenes from the variable Mg no. experiments were measured by counting 16 OH ions. Ignoring any matrix effects owing to variation in Mg no., H contents of olivine and pyroxene increase linearly with decreasing Mg no. At 6 GPa and 1200 °C, olivine H contents increase from 0.05 to 0.13 wt% H 2 O (8360 to 23 900 H/10 6 Si) as olivine Mg no. decreases from 100 to 68, and at 3 GPa and 1200 °C olivine H contents increase from 0.017 to 0.054 wt% (278 to 10 000 H/10 6 Si) as Mg no. decreases from 100 to 55. The partition coefficient for H between pyroxene and olivine, D H opx/ol , decreases from 1.05 at 3 GPa and 1200 °C to 0.61 at 6 GPa and 1200 °C. The storage capacity of Fe-rich olivines with compositions expected in the martian mantle is -1.5 times greater than those in the terrestrial mantle, suggesting that the geochemical behavior of H 2 O in the mantles of the two planets are quite similar. If 50% of the K 2 O on Mars remains in its mantle (Taylor et al. 2006), then a similar or greater proportion of the H 2 O is also in the mantle. Given accretionary models of the total martian H 2 O budget (Lunine et al. 2003), this suggests concentrations of 100-500 ppm H 2 O in the martian mantle and 0.1-1.9 wt% H 2 O in primary martian basalts.

April 2, 2015

Kinetics of thermal transformation of partially dehydroxylated pyrophyllite

Victor A. Drits, Arkadiusz Derkowski, Douglas K. McCarty

Page range: 1054-1069

Abstract

A multi-cycle heating and cooling thermogravimetric (TG) method was used to study the kinetic behavior of two partially dehydroxylated pyrophyllite samples. In the original state, the S076 sample contains only trans-vacant (tv) layers, whereas in sample S037 tv and cis-vacant (cv) layers are randomly interstratified. The method consists of consecutive heating cycles (rate 2 °C/min) separated by intervals of cooling to room temperature, with the maximum cycle temperature set (MCT) incrementally higher than in each previous cycle. The activation energy (E a ) values were calculated for the S037 and S076 samples for all cycles in terms of a homogeneous zero-order reaction with the regression coefficients r 2 ≥ 0.9997. The S076 sample had E a values that varied from 40 to 42 kcal/mol within a partial dehydroxylation (D T ) range from 19 to 63%. However, at D T values <19% and >63% the E a values are slightly lower at 38-39 kcal/mol and drop below 30 kcal/mol at D T = 90%. A bimodal distribution of the S037 sample E a values exists with increasing MCT and D T . In the first cycles of intense dehydroxylation from tv layers the E a values increase sharply from 34 kcal/mol at D T = 7% to 45 kcal/mol within the MCT interval from 525 to 575 °C and then decrease to 36-38 kcal/mol at the cycles with MCT = 650-700 °C. In the second portion of cycles corresponding to the dehydroxylation of cv layers, the E a values increase from 36-37 kcal/mol at MCT = 700 °C to 44-46 kcal/mol at MCT = 775 °C. These results show that both tv and cv layers require exactly the same energy for dehydroxylation and have similar variation of the E a values with MCT and D T . The pyrophyllite particle size distribution is a major factor that is likely responsible for a broad interval of dehydroxylation temperature. This implies that the lower the temperature, the smaller the particles that can be dehydroxylated. Therefore, the activation energy values at the beginning of the reaction are lower than those at higher degrees of dehydroxylation because of the combination of a slow experimental heating rate and thin crystallites, which both contribute to lower temperatures at which the reaction starts. The decrease in activation energy observed at the end of the dehydroxylation reaction of sample S076, and of the tv layer portion of sample S037 is accompanied by an increase in the “induction” temperature interval during which an accumulation of additional thermal energy decreases the activation energy. The kinetic parameters determined for the samples in this study correspond to a homogeneous reaction and are used to predict a general pattern of the structural transformations of pyrophyllite at different stages during dehydroxylation.

April 2, 2015

Dehydration of the natural zeolite goosecreekite CaAl₂Si₆O₁₆·5H₂O upon stepwise heating: A single-crystal and powder X-ray study

Eva Wadoski, Thomas Armbruster, Biljana Lazic, Martin Fisch

Page range: 1070-1078

Abstract

The zeolite mineral goosecreekite CaAl 2 Si 6 O 16 ⋅5H 2 O has been structurally investigated between 25 and 600 °C to monitor structural modifications upon partial dehydration. Temperature-dependent in situ powder and single-crystal X‑ray techniques were combined with TG/DTA experiments. Goosecreekite has a porous framework structure with well-ordered Si,Al distribution. In its natural form extraframework Ca is seven-coordinated. Up to ca. 100 °C, 1 H 2 O molecule is expelled reducing the Ca coordination from 7 to 6 accompanied by very minor changes of the tetrahedral framework. Depending on humidity and equilibration time a second structural change begins between 150 and 250 °C due to loss of additional 2.8 H 2 O pfu. The space group P2 1 is maintained but the c axis doubles and the structure is highly twinned. This new phase may be interpreted with a disordered model having two different framework topologies: one with the original T-O-T linkage and a second one with broken T-O-T links. Starting at ca. 300 °C, another 1.2 H 2 O are lost and this new orthorhombic, strongly contracted phase of P2 1 2 1 2 1 symmetry has five-coordinated Ca. The X‑ray powder signal of the orthorhombic phase persists up to 600 °C, but the structure becomes increasingly X‑ray amorphous until complete destruction at 675 °C. A single crystal (P2 1 phase with doubled c axis) partly dehydrated at 200 °C recovers the structure of natural goosecreekite under ambient conditions. Similar rehydration occurs after one month under ambient humidity for a powder sample of the orthorhombic P2 1 2 1 2 1 phase produced by heating of goosecreekite to 325 °C.

April 2, 2015

Incorporation mechanisms of Ta and Nb in zircon and implications for pegmatitic systems

Marieke Van Lichtervelde, Francois Holtz, Wanja Dziony, Thomas Ludwig, Hans-Peter Meyer

Page range: 1079-1089

Abstract

To investigate the processes that control Ta incorporation in zircon, two types of synthesis experiments were performed: (1) crystallization of zircon from an Li-Mo flux at 1 atm, and (2) crystallization of zircon (with or without coexisting tantalite) from a highly fluxed pegmatitic melt at 200 MPa and nearly water-saturated conditions. The first type of experiment is used to identify the influence of various doping elements (Hf, P, Al, and Mn) on Ta incorporation in zircon. These experiments reveal that P hinders the incorporation of Ta, whereas Al enhances Ta incorporation via charge balancing, and that Ta can be incorporated in the absence of any other doping element via the creation of vacancies in the zircon structure. Hafnium does not affect significantly Ta incorporation. Manganese and lithium do not enter the structure of zircon, except in the presence of P. Experiments with Nb show that the concentration of this element in zircon is nearly one order of magnitude lower than Ta (for similar Ta and Nb concentrations in the flux). The second type of experiments show how Ta is incorporated in zircon in natural granite and pegmatite systems. In those systems, P and Al have elevated concentrations, and P is preferentially incorporated in zircon via Al substitution to maintain charge balance. Below a P/Ta atomic ratio of ~10 in the melt, Ta competes with P for Al, and P is involved in a coupled substitution with Mn for charge balancing. Concentrations up to 3.7 wt% Ta 2 O 5 (0.03 apfu calculated to four atoms of oxygen) were measured in these zircon samples. The partition coefficients of Ta between melt and zircon are around 1 at 800-900 °C at conditions close to tantalite saturation. These results show that zircon incorporates significant amounts of Ta from the melt in P-poor peraluminous granites with a P/Ta atomic ratio lower than -10, which may ultimately affect the precipitation of Ta minerals. Such interactions between cations both in melts and in mineral structures are important to constrain in order to understand raremetal enrichment in granitic systems.

April 2, 2015

Variable-temperature ²⁷Al and ²⁹Si NMR studies of synthetic forsterite and Fe-bearing Dora Maira pyrope garnet: Temperature dependence and mechanisms of paramagnetically shifted peaks

Aaron C. Palke, Jonathan F. Stebbins

Page range: 1090-1099

Abstract

We present variable-temperature (VT, 31 to 204 °C) 29 Si magic angle spinning NMR (MAS-NMR) spectra of a synthetic forsterite containing dilute paramagnetic impurities and 27 Al and 29 Si spectra of two iron-bearing natural pyrope garnet specimens from the Dora Maira ultrahigh-pressure metamorphism locality. Previous NMR studies of these materials reported multiple “anomalous” resonances outside the range of expected frequencies. It has been hypothesized that these peaks were caused by interactions between paramagnetic centers and the resonating nuclei. Our VT MAS-NMR study shows a linear relationship between peak position and inverse temperature for the “anomalous” resonances, confirming their assignment as paramagnetic shifts. A detailed analysis of the peaks in the pyropes indicates that the “anomalous” resonances are caused by a combination of the Fermi contact and pseudocontact interactions. The paramagnetic shifts in the 29 Si spectra are likely caused by Fe 2+ in the first, second, and third nearest dodecahedral sites while those in the 27 Al spectra are likely caused by one or two Fe 2+ in the first shell dodecahedral site.

April 2, 2015

Calibrating Ti concentrations in quartz for SIMS determinations using NIST silicate glasses and application to the TitaniQ geothermobarometer

Whitney M. Behr, Jay B. Thomas, Richard L. Hervig

Page range: 1100-1106

Abstract

The recently developed titanium-in-quartz (TitaniQ) geothermobarometer of Wark and Watson (2006) and Thomas et al. (2010) has the potential to be applied to a wide range of igneous and metamorphic rocks. For Ti concentrations > -10 ppm, the concentrations can be measured using an electron microprobe, but lower concentrations are below detection limits and require techniques such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS). SIMS is ideal for this purpose as it maximizes lateral and depth resolution. We used SIMS to analyze synthetic quartz crystals characterized for Ti concentration by electron probe (18-813 ppm Ti) and compare this calibration to the commonly available NIST 61X glasses using both high mass resolution (HMR) and conventional energy filtering (CEF) techniques. We used a primary beam of 16 O - ions and detected positive secondary ions. During HMR sessions, the mass spectrometer was operated at a mass resolving power (M/ΔM) of ~2000 to separate molecular ions from elemental Ti peaks. For CEF analyses, the instrument detected secondary ions sputtered from the sample with excess kinetic energies of 75 ± 20 eV. Titanian quartz measurements reveal general homogeneity and a linear increase in Ti + /Si + ion ratios with increasing Ti concentrations. Background signals represent 0-1 ppm. The slopes of the calibration curves for the titanian quartz crystals are -70% of the curves constructed using NIST glasses, indicating a much higher ion yield for Ti from the glasses compared to the simple oxide of silicon. We demonstrate, however, that a simple correction factor allows NIST glasses to be used to quantitatively determine the Ti concentrations of quartz (with 3.8% error using HMR, and 8.2% error using CEF) until homogenous, well-characterized samples of SiO 2 become generally available.

April 2, 2015

Crystal structure of Na₃Fe(SO₄)₃: A high-temperature product (∼400 °C) of sideronatrite [Na₂Fe(SO₄)₂OH⋅3H₂O]

Fernando Scordari, Gennaro Ventruti, Alessandro F. Gualtieri, Andrea Lausi

Page range: 1107-1111

Abstract

The iron sulfate Na 3 Fe(SO 4 ) 3 studied here has been obtained as a high-temperature (HT) product (-400 °C) from the thermal decomposition of sideronatrite from Sierra Gorda (Chile) having composition Na 2 Fe(SO 4 ) 2 (OH)⋅3H 2 O. The structure determination was carried out using synchrotron X‑ray powder diffraction. Structural data refined by the Rietveld method, up to R p = 11.95%, are: space group R3̅, lattice parameters a = b = 13.6231(1) Å and c = 9.0698(1) Å, V = 1457.76(2) Å 3 , and Z = 6. The structure of Na 3 Fe(SO 4 ) 3 can be described in terms of FeO 6 octahedra connected to sulfate tetrahedra by corner-sharing to form infinite chains [Fe(SO 4 ) 3 ] ∞ , running along c. These chains are joined together by Na atoms to build up a three-dimensional network of strong (Fe-O-S) and weak (Na-O) bonds. The topological relationships of Na 3 Fe(SO 4 ) 3 to the structure of some analog minerals are also discussed.

April 2, 2015

Evidence for boron incorporation into the serpentine crystal structure

Sonja Pabst, Thomas Zack, Ivan P. Savov, Thomas Ludwig, Detlef Rost, Edward P. Vicenzi

Page range: 1112-1119

Abstract

Serpentinite mud volcanoes from the Mariana forearc comprise B-rich mantle wedge peridotites serpentinized by slab fluids. The major component of these rocks are serpentine group minerals [Mg 3 Si 2 O 5 (OH) 4 ], showing highly variable textural and geochemical features. Micro-Raman spectroscopy reveals that the serpentine minerals are well-crystallized lizardite and chrysotile. In situ SIMS spot analyses and element mapping via ToF-SIMS show that B is evenly distributed across serpentine grains, suggesting that serpentine, both lizardite and chrysotile in different textural regions, can host significant amounts of B (up to -200 μg/g) into its crystal structure. As such structurally bound B can only be released during recrystallization or serpentine breakdown, our results have implications for modeling of the efficiency of cross-arc fluid mobile element recycling in subduction zones and stress the importance of the hydrated forearc mantle as a reservoir for fluid mobile elements.

April 2, 2015

Structure refinement of Ag-free heyrovskýite from Vulcano (Aeolian Islands, Italy)

D. Pinto, T. Balić-Žunić, A. Garavelli, F. Vurro

Page range: 1120-1128

Abstract

The first single-crystal structure refinement of Ag- and Cu-free heyrovskýite was performed in this study. Crystals investigated were sampled from the high-temperature fumaroles of La Fossa crater of Vulcano, Aeolian Islands, Italy. Electron microprobe analyses gave the average chemical formula (Pb 5.86 Cd 0.03 ) Σ5.89 Bi 2.04 (S 8.52 Se 0.53 Cl 0.03 ) Σ9.08 , which is very close to the ideal composition of heyrovskýite, Pb 6 Bi 2 S 9 . Lattice parameters are a = 13.7498(4), b = 31.5053(8), c = 4.1475(1) Å, V = 1796.7(1) Å 3 , space group Bbmm. The structure refinement converges to R = 4.17% for 1312 reflections with F o > 4σ(F o ). In Ag-free heyrovskýite from Vulcano, as well as in the synthetic Pb 6 Bi 2 S 9 , the trigonal prismatic coordinated position Me1, as well as the octahedrally coordinated position Me3 are occupied only by Pb. Me2, also octahedrally coordinated, is dominated by Pb, whereas the octahedra situated at the edges of the octahedral layers (Me4 and Me5) are centered around mixed (Pb,Bi) positions, with almost equal occupancy. The octahedrally coordinated site Me3 was found to incorporate vacancies (□), created by the substitution 3Pb 2+ → 2Bi 3+ +□, which allows for the observed deviations from the ideal composition, Pb 6 Bi 2 S 9 . Selenium is preferentially ordered at the fivefold-coordinated anionic sites. Taking into account vacancies, as well as Se for S substitutions the structural formula of Ag-free heyrovskýite from Vulcano is Pb 5.82 Bi 2.12 □ 0.06 S 8.70 Se 0.30 . Comparison with the Ag-bearing heyrovskýite structures shows that during the 2 Pb → Ag(Cu)+Bi substitution the increased content of Bi is incorporated preferentially in the Me5 site until 2/3 Bi occupancy and thereafter in the two central octahedrally coordinated sites (Me2 and Me3). Silver occupies exclusively marginal octahedrally coordinated Me4 site like in the other members of the lillianite homologous series. The observed crystal chemical characteristics of the Ag-free heyrovskýite are in accordance with a model suggested by Callegari and Boiocchi, which describes the monoclinic form, aschamalmite, as an ordered polymorph of Pb 6 Bi 2 S 9 , and heyrovskýite as a fully disordered polymorph of the same compound. Ag incorporation is expected to increase the Pb/Bi disorder and to stabilize the orthorhombic heyrovskýite form.

April 2, 2015

Microtextures, microchemistry, and mineralogy of basaltic glass alteration, Jeju Island, Korea, with implications for elemental behavior

Gi Young Jeong, Young Kwan Sohn

Page range: 1129-1147

Abstract

The meteoric alteration of basaltic glass in hyaloclastite (0.55 to 0.2 Ma) from Jeju Island, Korea, was examined using high-resolution electron microscopy, in situ sample preparation using focused ion beam, and microchemical analysis. The glass particles showed a sequential development of alteration textures toward the glass interior as follows: oscillatory zoning of smectite and amorphous bands/hemispheres, congruent dissolution of glass with smectite infilling in interparticle pore, and the replacement of nanogranular amorphous aggregate (NAA) for porous leached glass (LG) followed by a partial crystallization of smectite. Chemical compositions of LG widely varied from partial to complete leaching of almost all kinds of cations, to a preferred leaching of Na only. The order of leaching in LG followed Na + >Mg 2+ >Ca 2+ = Fe 2+ >Al 3+ >Ti 4+ . Leached cations were removed from the hyaloclastite-water system or incorporated into secondary phases. Sodium was all but removed from the system. Magnesium was largely lost with partial incorporation into smectite. Calcium was significantly retained in NAA, partly incorporated into the smectite interlayer, and partly lost. Iron and Al were partitioned between NAA and smectite. Titanium was mostly retained in NAA and Ti-rich silicates. The molar ratio of major cations to Si was reversed from Ca 2+ >Mg 2+ >Na + in basaltic glass to Na + >Mg 2+ >Ca 2+ in groundwater. The geochemical evolution of pore water was influenced by the microtextural and microchemical evolution of glass particles, and vice versa. Systematic microtextural, microchemical, and mineralogical analyses of natural glass alteration are critical to understanding the long-term behavior of glass alteration.

April 2, 2015

Orientation of channel carbonate ions in apatite: Effect of pressure and composition

Michael E. Fleet, Xiaoyang Liu, Xi Liu

Page range: 1148-1157

Abstract

X-ray structure and FTIR spectroscopy evidence is reviewed for two separate orientations of carbonate ions in the c-axis channel of carbonate apatite (CHAP) synthesized at high pressure and temperature: A1 carbonate has two O atoms close to the c-axis, whereas A2 carbonate has only one. The A2 orientation is reevaluated and its local structure refined using a rigid body model. A2 is the high-pressure configuration, but the A1 → A2 transformation is also dependent on bulk composition, especially the presence of type B carbonate. In the dry CaO-P 2 O 5 -CO 2 system, the A1 → A2 transformation is initiated beyond about 4 GPa in type A CHAP compared with 1-2 GPa in A-B CHAP. Also, A2 carbonate is only weakly present in Na-bearing A-B CHAP synthesized at 0.5-1 GPa, which is assumed to be close to the threshold pressure for the transformation. The pressure stability of A2 is believed to be related to its central location in the channel and equitable distribution of bond distances to Ca2 cations in the channel wall (2.25 to 2.54 Å).

April 2, 2015

Thermoelastic property and high-pressure stability of Fe₇C₃: Implication for iron-carbide in the Earth’s core

Yoichi Nakajima, Eiichi Takahashi, Nagayoshi Sata, Yu Nishihara, Kei Hirose, Kenichi Funakoshi, Yasuo Ohishi

Page range: 1158-1165

Abstract

To investigate the physical property of Fe 7 C 3 , we carried out in situ X‑ray diffraction experiments using a Kawai-type multi-anvil apparatus and a diamond anvil cell up to 71.5 GPa and 1973 K. The carbide was found to be stable under these experimental conditions. However, we found anomalous behavior in its isothermal compression and thermal expansivity. These anomalies could be due to the magnetic phase transition in Fe 7 C 3 from a ferromagnetic (fm) to a paramagnetic (pm) phase. The Curie temperature of 523 K at 1 bar (Tsuzuki et al. 1984) decreases with pressure, and the pressure-induced magnetic transition is estimated to occur at ~18 GPa and 300 K. The pressure-volume-temperature (P-V-T) data set for the pm-Fe 7 C 3 was fitted by the Mie-Grüneisen-Debye (MGD) equation of state (EOS) and the following parameters were obtained: unit-cell volume V 0 = 184.2 ± 0.3 Å 3 , bulk modulus K 0 = 253 ± 7 GPa, the pressure derivative of bulk modulus K' 0 = 3.6 ± 0.2, Grüneisen parameter γ 0 = 2.57 ± 0.05, Debye temperature θ 0 = 920 ± 140 K, and q = 2.2 ± 0.5, respectively, at zero pressure. The calculated density for Fe 7 C 3 provides a good explanation for the density of the Earth’s inner core obtained from seismological observations.

April 2, 2015

Yttriaite-(Y): The natural occurrence of Y₂O₃ from the Bol’shaya Pol’ya River, Subpolar Urals, Russia

Stuart J. Mills, Pavel M. Kartashov, Chi Ma, George R. Rossman, Margarita I. Novgorodova, Anthony R. Kampf, Mati Raudsepp

Page range: 1166-1170

Abstract

Yttriaite-(Y), ideally Y 2 O 3 , is a new mineral (IMA2010-039) from the alluvial deposits of the Bol’shaya Pol’ya River, Subpolar Urals, Russia. The new mineral occurs as isolated crystals, typically cubo-octahedra <6 μm in size, embedded in massive native tungsten. Associated minerals include: copper, zircon, osmium, gold, and pyrite. The main forms observed are {100} and {111}. Due to the crystal size, physical properties could not be determined; however, the properties of synthetic Y 2 O 3 are well known. Synthetic Y 2 O 3 crystals are colorless to white with a white streak; crystals are transparent with an adamantine luster, while massive Y 2 O 3 is typically translucent with an earthy luster. Synthetic Y 2 O 3 has a Vickers hardness of 653.91, which corresponds to 5.5 on the Mohs scale. Synthetic Y 2 O 3 crystals have good cleavage on {111}. Yttriaite-(Y) is isotropic; the refractive index measured at 587 nm on synthetic Y 2 O 3 is n = 1.931. The empirical chemical formula (mean of 4 electron microprobe analyses) calculated on the basis of 3 O is: Y 1.98 Dy 0.01 Yb 0.01 O 3 . Yttriaite-(Y) is cubic, space group Ia3̅, with parameters a = 10.6018(7) Å, V = 1191.62(7) Å 3 , and Z = 16. The five strongest lines in the powder X-ray diffraction pattern (measured on synthetic Y 2 O 3 using synchrotron radiation) are [d obs in Å (I) (hkl)]: 3.0646 (100) (222), 1.8746 (55) (440), 1.5984 (38) (622), 2.6537 (26) (400), and 4.3356 (14) (211). The mineral name is based on the common name for the chemical compound, yttria.

April 2, 2015

Identification and characterization of nanosized tripuhyite in soil near Sb mine tailings

Satoshi Mitsunobu, Yoshio Takahashi, Satoshi Utsunomiya, Matthew A. Marcus, Yasuko Terada, Takeru Iwamura, Masahiro Sakata

Page range: 1171-1181

Abstract

In soil near tailings from an antimony (Sb) mine, we found micro-grains coated with an antimonyrich layer. These grains were characterized in detail using multiple advanced analytical techniques such as micro-X‑ray absorption near edge structure (μ-XANES), micro-extended X‑ray absorption fine structure (μ-EXAFS), micro-X‑ray diffraction (μ-XRD), transmission electron microscope (TEM), and electron probe microanalysis (EPMA). The EPMA showed that one soil grain (grain A) locally accumulated a large amount of Sb in the secondary phases (40-61 wt% Sb 2 O 5 ) with significant Fe (20-28 wt% Fe 2 O 3 ). The spatial distribution of Sb in the grain was similar to that of iron. Both Fe μ-XANES and μ-XRD of the Sb hot spots in grain A consistently showed that the secondary products were dominantly composed of ferric antimonate, tripuhyite (FeSbO 4 ). Fits to the Sb K-edge μ-EXAFS of this phase showed second-neighbor coordination numbers -30% smaller than in bulk tripuhyite, indicating that the tripuhyite included in grain A is nanoparticulate and/or has a high structural disorder. The TEM analysis suggests that the particle size of tripuhyite in grain A was around 10 nm, which is consistent with the size range indicated by μ-XRD and μ-EXAFS. This is the first report showing tripuhyite with nanocrystallinity in natural soil to date.

April 2, 2015

Letter. High-pressure I2/c-P2₁/c phase transformation in SrAl₂Si₂O₈ feldspar

Francesco Pandolfo, Tiziana Boffa Ballaran, Fabrizio Nestola, Monika Koch Müller, Maria Mrosko, Emiliano Bruno

Page range: 1182-1185

Abstract

In situ, high-pressure single-crystal X‑ray diffraction experiments were performed on a feldspar with composition SrAl 2 Si 2 O 8 (space group I2/c). The measurements were performed at 19 different pressures up to 7.9 GPa. The unit-cell parameters and the unit-cell volume show a strong discontinuity at 6.6 GPa indicating a first-order phase transition. The systematic absences clearly show that the transition occurs from I2/c to P2 1 /c space group symmetry, as for the transition recently reported for a feldspar with composition Sr 0.8 Ca 0.2 Al 2 Si 2 O 8 . Our results suggest that the P2 1 /c phase is softer than the I2/c one. Moreover, within the I2/c symmetry two pressure-volume trends are evident due to a volume softening above 4.2 GPa. The softening did not allow fitting the data to a single equation of state, and only the data up to 3.67 were fitted with a third-order Birch-Murnaghan equation of state. Based on our and previous experimental results we propose a possible composition-pressure stability field for the Sr-rich side along the CaAl 2 Si 2 O 8 -SrAl 2 Si 2 O 8 join.

April 2, 2015

Letter. Crystal structure of uchucchacuaite, AgMnPb₃Sb₅S₁₂, and its relationship with ramdohrite and fizélyite

H. Yang, R.T. Downs, S.H. Evans, M.N. Feinglos, K.T. Tait

Page range: 1186-1189

Abstract

Uchucchacuaite, ideally AgMnPb 3 Sb 5 S 12 , was originally reported as orthorhombic, with possible space group Pmmm, P222, or Pmm2, and unit-cell parameters a = 12.67, b = 19.32, and c = 4.38 Å obtained from powder X‑ray diffraction data (Moëlo et al. 1984a). Using single-crystal X‑ray diffraction, we examined two uchucchacuaite samples, one from the type locality, Uchucchacua, Peru, and the other from Hokkaido, Japan (designated as R100213 and R070760, respectively). Our results show that uchucchacuaite is isostructural with ramdohrite and fizélyite, with monoclinic symmetry (P2 1 /n) and the unit-cell parameters a = 19.3645(11), b = 12.7287(8), c = 8.7571(6) Å, β = 90.059(3)° for R100213 and a = 19.3462(7), b = 12.7251(5), c = 8.7472(3) Å, β = 90.017(2)° for R070760. Both samples are pervasively twinned and the twin refinements yielded the final R1 factors of 0.037 and 0.031 for R100213 and R070760, respectively. The chemical compositions determined from electron microprobe analysis are Ag 0.99 (Mn 0.92 Pb 0.03 Sb 0.02 Bi 0.01 ) Σ=0.98 Pb 3.00 Sb 5.00 S 12.00 for R100213 and Ag 1.00 (Mn 0.82 Sb 0.11 Ag 0.04 Bi 0.02 ) Σ=0.99 Pb 2.98 Sb 5.00 S 12.00 for R070760. The key structural difference among uchucchacuaite, ramdohrite, and fizélyite lies in the cations occupying the M2 site, which can be expressed with a general structural formula as Ag(M 2+ 2y Ag ½-y Sb ½-y )Pb 3 Sb 5 S 12 , where M 2+ represents divalent cations with 0 ≤ y ≤ ½. From the current list of IMA-defined minerals, we consider M = Cd with y = 0.125 for ramdohrite, M = Pb with y = 0.25 for fizélyite, and M = Mn with y = 0.5 for uchucchacuaite. Associated with the variation in the average M2 cation size from fizélyite (1.078 Å) to ramdohrite (0.955 Å) and uchucchacuaite (0.83 Å) is the significant decrease in the average M2-S bond distance from 2.917 to 2.834, and 2.654 Å, respectively, as well as corresponding variations in the unit-cell b dimension from ~13.23 to 13.06 and 12.73 Å.

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American Mineralogist: Journal of Earth and Planetary Materials (Am Min), is the flagship journal of the Mineralogical Society of America (MSA), continuously published since 1916. Am Min is home to some of the most important advances in the Earth Sciences. Our mission is a continuance of this heritage: to provide readers with reports on original scientific research, both fundamental and applied, with far reaching implications and far ranging appeal. Topics of interest cover all aspects of planetary evolution, and biological and atmospheric processes mediated by solid-state phenomena. These include, but are not limited to, mineralogy and crystallography, high- and low-temperature geochemistry, petrology, geofluids, bio-geochemistry, bio-mineralogy, synthetic materials of relevance to the Earth and planetary sciences, and breakthroughs in analytical methods of any of the aforementioned.

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Volume 96 Issue 7

Issue of American Mineralogist

Needs and opportunities in mineral evolution research

Abstract

Rutile inclusions in quartz crystals record decreasing temperature and pressure during the exhumation of the Su-Lu UHP metamorphic belt in Donghai, East China

Abstract

A first-principles study of the phase transition from Holl-I to Holl-II in the composition KAlSi3O8

Abstract

Sejkoraite-(Y), a new member of the zippeite group containing trivalent cations from Jáchymov (St. Joachimsthal), Czech Republic: Description and crystal structure refinement

Abstract

Thermoelastic and thermodynamic properties of plagioclase feldspars from thermal expansion measurements

Abstract

Quantitative determination of chrysotile in massive serpentinites using DTA: Implications for asbestos determinations

Abstract

In situ observation of the crystallization pressure induced by halite crystal growth in a microfluidic channel

Abstract

Microstructures of the larval shell of a pearl oyster, Pinctada fucata, investigated by FIB-TEM technique

Abstract

Magnesium quantification in calcites [(Ca,Mg)CO3] by Rietveld-based XRD analysis: Revisiting a well-established method

Abstract

The effect of Fe on olivine H2O storage capacity: Consequences for H2O in the martian mantle

Abstract

Kinetics of thermal transformation of partially dehydroxylated pyrophyllite

Abstract

Dehydration of the natural zeolite goosecreekite CaAl2Si6O16·5H2O upon stepwise heating: A single-crystal and powder X-ray study

Abstract

Incorporation mechanisms of Ta and Nb in zircon and implications for pegmatitic systems

Abstract

Variable-temperature 27Al and 29Si NMR studies of synthetic forsterite and Fe-bearing Dora Maira pyrope garnet: Temperature dependence and mechanisms of paramagnetically shifted peaks

Abstract

Calibrating Ti concentrations in quartz for SIMS determinations using NIST silicate glasses and application to the TitaniQ geothermobarometer

Abstract

Crystal structure of Na3Fe(SO4)3: A high-temperature product (∼400 °C) of sideronatrite [Na2Fe(SO4)2OH⋅3H2O]

Abstract

Evidence for boron incorporation into the serpentine crystal structure

Abstract

Structure refinement of Ag-free heyrovskýite from Vulcano (Aeolian Islands, Italy)

Abstract

Microtextures, microchemistry, and mineralogy of basaltic glass alteration, Jeju Island, Korea, with implications for elemental behavior

Abstract

Orientation of channel carbonate ions in apatite: Effect of pressure and composition

Abstract

Thermoelastic property and high-pressure stability of Fe7C3: Implication for iron-carbide in the Earth’s core

Abstract

Yttriaite-(Y): The natural occurrence of Y2O3 from the Bol’shaya Pol’ya River, Subpolar Urals, Russia

Abstract

Identification and characterization of nanosized tripuhyite in soil near Sb mine tailings

Abstract

Letter. High-pressure I2/c-P21/c phase transformation in SrAl2Si2O8 feldspar

Abstract

Letter. Crystal structure of uchucchacuaite, AgMnPb3Sb5S12, and its relationship with ramdohrite and fizélyite

Abstract

A first-principles study of the phase transition from Holl-I to Holl-II in the composition KAlSi₃O₈

Magnesium quantification in calcites [(Ca,Mg)CO₃] by Rietveld-based XRD analysis: Revisiting a well-established method

The effect of Fe on olivine H₂O storage capacity: Consequences for H₂O in the martian mantle

Dehydration of the natural zeolite goosecreekite CaAl₂Si₆O₁₆·5H₂O upon stepwise heating: A single-crystal and powder X-ray study

Variable-temperature ²⁷Al and ²⁹Si NMR studies of synthetic forsterite and Fe-bearing Dora Maira pyrope garnet: Temperature dependence and mechanisms of paramagnetically shifted peaks

Crystal structure of Na₃Fe(SO₄)₃: A high-temperature product (∼400 °C) of sideronatrite [Na₂Fe(SO₄)₂OH⋅3H₂O]

Thermoelastic property and high-pressure stability of Fe₇C₃: Implication for iron-carbide in the Earth’s core

Yttriaite-(Y): The natural occurrence of Y₂O₃ from the Bol’shaya Pol’ya River, Subpolar Urals, Russia

Letter. High-pressure I2/c-P2₁/c phase transformation in SrAl₂Si₂O₈ feldspar

Letter. Crystal structure of uchucchacuaite, AgMnPb₃Sb₅S₁₂, and its relationship with ramdohrite and fizélyite