Volume 100, Issue 7

Leaps forward in analytical technology often stimulate major discoveries in geochemistry. In some cases, the improvements are in sensitivity and precision. For example, recent measurements of minute variations in 142 Nd, 182 W, and U-series (to name a few) have revolutionized our understanding of terrestrial and planetary geochemical evolution. In other cases, the improvements are in the spatial scale of the analysis. Isotopic analysis of individual melt inclusions, single shell layers in mollusks and zoning layers in zircons, all have provided fundamental insights into geologic processes. Historically, whenever we look more closely at the composition of materials, we find unexpected features. These variations often are mystifying at first (see all of the above) and often somewhat unwelcome (too much information!). But it is precisely such new, headache-producing details that provide new insights into geological processes. On page 1355, Valley and colleagues use a promising new analytical method called atom probe tomography (APT) to analyze one of the oldest materials on the planet [Jack Hills zircons (Wilde et al. 2001; Valley et al. 2014)]. APT has a unique combination of spatial and geochemical analytical capabilities, which Valley et al. use to confirm the Hadean age of the zircons, and to gain new insights into their thermochronologic history. This is one of the first geochemical studies to use APT, and offers an early glimpse of future research paths.

Silicate melt inclusions (SMIs) are a very reliable tool for reconstructing the composition of magma (silicate melt + volatiles) and tracing its evolution from mantle depths to the Earth’s surface. Although the scientific community already knew about the ability of shrinkage bubbles in SMIs to trap a significant fraction of CO 2 , quantitative estimates were still lacking. In the article “Melt inclusion CO 2 contents, pressures of olivine crystallization, and the problem of shrinkage bubbles” by Wallace et al. (2015) (included in the special collection “Glasses, melts, and fluids, as tools for understanding volcanic processes and hazards”) the authors provide a numerical estimate of the amount of initial CO 2 dissolved in the melt that is lost to shrinkage bubbles and a computational method to estimate such an amount in absence of experimental studies and direct measurements by micro-Raman spectroscopy.

As the American Mineralogist and the Mineralogical Society of America (MSA) approach their centennials, troubling indicators cast a shadow on the future of the mineralogical sciences. These indicators include decreases in grant funding for research in mineralogical disciplines, a lack of attention to mineral resources, trends in Ph.D.’s awarded in the Earth sciences, and the lack of emphasis on the Earth sciences in state educational policies. Some of these problems can be traced to a lack of scientific literacy among the public and policy makers. Others can be attributed to actions or inactions by those whose research or teaching involves minerals. MSA and its members must do more to educate students, colleagues, and the public about the mineralogical sciences and their importance to the well being of society. If we are proactive and imaginative in promoting our science, the “future of mineralogy” can be assured.

This paper reviews experimental nuclear magnetic resonance (NMR) and computational molecular dynamics (MD) investigations of the structural and dynamical behavior of cations, anions, H 2 O, and CO 2 on the surfaces and in the interlayer galleries of layer-structure minerals and their composites with polymers and natural organic matter (NOM). The interaction among mineral surfaces, chargebalancing cations or anions, H 2 O, CO 2 , and NOM are dominated by Coulombic, H-bond, and van der Waals interactions leading to statically and dynamically disordered systems and molecular-scale processes with characteristic room-temperature frequencies varying from at least as small as 102 to >1012 Hz. NMR spectroscopy provides local structural information about such systems through the chemical shift and quadrupolar interactions and dynamical information at frequencies from the subkilohertz to gigahertz ranges through the T 1 and T 2 relaxation rates and line shape analysis. It is often difficult to associate a specific structure or dynamical process to a given NMR observation, however, and computational molecular modeling is often effective in providing a much more detailed picture in this regard. The examples discussed here illustrate these capabilities of combining experimental NMR and computational modeling in mineralogically and geochemically important systems, including clay minerals and layered double hydroxides.

Atom-probe tomography (APT) and secondary ion mass spectrometry (SIMS) provide complementary in situ element and isotope data in minerals such as zircon. SIMS measures isotope ratios and trace elements from 1-20 μm spots with excellent accuracy and precision. APT identifies mass/ charge and three-dimensional position of individual atoms (±0.3 nm) in 100 nm-scale samples, volumes up to one million times smaller than SIMS. APT data provide unique information for understanding element and isotope distribution; crystallization and thermal history; and mechanisms of mineral reaction and exchange. This atomistic view enables evaluation of the fidelity of geochemical data for zircon because it provides new understanding of radiation damage, and can test for intracrystalline element mobility. Nano-geochronology is one application of APT in which Pb isotope ratios from sub-micrometer domains of zircon provide model ages of crystallization and identify later magmatic and metamorphic reheating. Based on SEM imaging and SIMS analysis, 11 needle-shaped specimens ~100 nm in diameter were sampled from one Archean and two Hadean zircons by focused ion-beam milling and analyzed with APT. The three-dimensional distribution of Pb and nominally incompatible elements (Y, REEs) differs at the atomic scale in each zircon. Zircon JH4.0 (4.007 Ga, Jack Hills, Western Australia) is homogeneous in Pb, Y, and REEs. In contrast, Pb and Y and REEs are clustered in sub-equant ~10 nm diameter domains, spaced 10-40 nm apart in zircons ARG2.5 (2.542 Ga, Grouse Creek Mountains, Utah) and JH4.4 (4.374 Ga, Jack Hills). Most clusters are flattened parallel to (100) or (010). U and Th are not collocated with Pb in clusters and appear to be homogeneously distributed in all three zircons. The analyzed domains experienced 4 to 8 × 10 15 α-decay events/mg due to U and Th decay and yet all zircons yield U-Pb ages by SIMS that are better than 97% concordant, consistent with annealing of most radiation damage. The 207 Pb/ 206 Pb ratios for the 100 nm-scale specimens measured by APT average 0.17 for ARG2.5, 0.42 for the JH4.0, and 0.52 for JH4.4. These ratios are less precise (±10-18% 2σ) due to the ultra-small sample size, but in excellent agreement with values measured by SIMS (0.1684, 0.4269, and 0.5472, respectively) and the crystallization ages of the zircons. Thus Pb in these clusters is radiogenic, but unsupported, meaning that the Pb is not spatially associated with its parent isotopes of U and Th. For the domain outside of clusters in JH4.4, the 207 Pb/ 206 Pb ratio is 0.3, consistent with the SIMS value of 0.2867 for the zircon overgrowth rim and an age of 3.4 Ga. In ARG2.5, all Pb is concentrated in clusters and there is no detectable Pb remaining outside of the clusters. The Pb-YREE- rich clusters and lack of correlation with U in ARG2.5 and JH4.4 are best explained by diffusion of Pb and other elements into ~10 nm amorphous domains formed by α-recoil. Diffusion distances of ~20 nm for these elements in crystalline zircon are consistent with heating at temperatures of 800 °C for ~2 m.y. Such later reheating events are identified and dated by APT from 207 Pb/ 206 Pb model ages of clusters in JH4.4 and by the absence of detectable Pb outside of clusters in ARG2.5. SIMS datesfor the zircon rims independently confirm reheating of ARG2.5 and JH4.4, which were xenocrysts in younger magmas when rims formed. It is proposed that most domains damaged by α-recoil were annealed at ambient temperatures above 200-300 °C before reheating and only a small number of domains were amorphous and available to concentrate Pb at the time of reheating. The size, shapes, and orientations of clusters were altered by annealing after formation. The absence of enriched clusters in JH4.0 shows that this zircon was not similarly reheated. Thus APT data provide thermochronologic information about crustal reworking even for zircons where no overgrowth is recognized. The clusters in JH4.4 document Pb mobility at the sub-50 nm scale, but show that the much larger 20 μm-scale domains analyzed by SIMS were closed systems. The reliability of oxygen isotope ratios and other geochemical data from zircon can be evaluated by these means. These results verify the age of this zircon and support previous proposals that differentiated crust existed by 4.4 Ga and that the surface of Earth was relatively cool with habitable oceans before 4.3 Ga. These analytical techniques are of general applicability to minerals of all ages and open many new research opportunities.

Metamict minerals contain uranium and thorium, which contribute to physical degradation or metamictization of their crystal structures over geologic time. The damage occurs primarily through progressive overlapping recoil nuclei collision cascades from ɑ-decay of 238 U, 232 Th, 235 U, and their daughter products. We measured 222 Rn and 220 Rn emanations from metamict samples of nine oxides (brannerite, davidite, fergusonites, pyrochlores, samarskites, and uraninite), two phosphates (monazites), and eight silicates (cerite, gadolinites, perrierite, rinkite, thorite, turkestanite, and vesuvianite). The total absorbed a-doses ranged from 1.4 × 10 15 to 6.1 × 10 18 a-decay mg-1 for cerite and uraninite, respectively. The 222 Rn emanation coefficients varied from 5 × 10 -5 % (uraninite) to 2.5% (turkestanite). The 220 Rn emanation coefficients varied from 7 × 10 -3 % (gadolinite Ytterby) to 6.2% (gadolinite Marysin). The lowest 222 Rn emanation coefficients occurred among metamict minerals containing the highest concentrations of 238 U (i.e., uraninite, samarskites, and brannerite). Overall, the 222 Rn and 220 Rn emanation coefficients observed in this study fall significantly below previously reported values.

The Athabasca Basin hosts world class uranium deposits, such as the McArthur River deposit. This paper presents the occurrence of aluminum phosphate-sulfate (APS) minerals in the metasedimentary rocks along the P2 fault, the main ore-hosting fault of the McArthur River deposit. It compares the APS minerals along the P2 fault with those outside the fault, examined in this study, and those from other deposits of the Athabasca Basin and from other Paleo- to Mesoproterozoic basins worldwide. APS minerals are common along the P2 fault but rare outside of the P2 fault zone in the basement and along the unconformity between the Athabasca sandstones and the basement. The APS minerals along the P2 fault occur with sudoite (± illite, magnesiofoitite) and are zoned with Sr-, Ca-, and S-rich cores (solid solution between svanbergite, crandallite, and goyazite) and LREE- and P-rich rims (close to florencite composition). APS minerals in the Bleached Zone (altered rocks along the unconformity consisting predominantly of kaolin and illite) are Sr-, Ca-, and S-rich (high svanbergite component) and occur with kaolin. APS minerals in the Red-Green Zone (mingled red hematitic and green chloritic basement rocks below the Bleached Zone) occur with sudoite and clinochlore. They contain relict cores of LREE- and As-rich arsenoflorencite-(Ce) and rims of svanbergite-goyazite-crandallite solid solution. The occurrence of svanbergite-crandallite-goyazite along the unconformity suggests their formation by relatively oxidizing fluids during diagenesis of the overlying sandstones. The relict cores of arsenoflorencite-(Ce) in the Red-Green Zone are interpreted to be the product of paleo-weathering before the deposition of the Athabasca sandstones. Florencitic APS minerals are found along the entire studied strike length (7 km) of the P2 fault, including the ore zone and non-mineralized areas, but are absent outside the fault zone. The florencitic APS minerals contain low SO 4 2- in the ore zone, suggesting relatively reducing conditions during their crystallization. Zoned APS minerals (with svanbergitic cores and florencitic rims) proximal to ore contain elevated U (up to 16 ppm). These features suggest that diagenetic, oxidizing, and uranium-bearing fluids traveled along the P2 fault and became relatively reduced, especially within the ore zone. It also suggests florencitic APS minerals are contemporaneous with uranium mineralization. The restricted occurrence of florencitic APS mineral along the P2 fault in the basement suggests their use in identifying fertile basement structures associated with uranium mineralization.

The hydrogen mobility in andradite single crystals from an iron-skarn deposit was investigated through H-D and D-H exchange experiments. Thin slices were annealed in a horizontal furnace flushed with a gas mixture of Ar/D 2(10%) and Ar/H 2(10%) at ambient pressure between 400 and 700 °C. FTIR analyses were performed before and after each annealing run. Between 15 and 35% of the original OH content remained in the crystal structure at the end of the deuteration experiments. This contrasts with the results of similar experiments performed in other NAMs, where all hydrogen atoms are replaced by deuterium in the structure. However, because a steady state was reached at the end of the experiments, the diffusion law for the exchange process was determined as: D H-D = D 0 exp[-(96 ± 11) kJ/mol/RT], with logD 0 = -5.9 ± 0.7 (in m 2 /s). The activation energy is similar to that for hydrogen diffusion in grossular, but H diffusivity is more than two orders of magnitude faster. Our results demonstrate that, because major element composition has a major effect on H-D diffusion laws, it must be considered in any discussion of δD signatures in garnets. In andradite-rich garnets, hydrogen isotope data can only be used to record short, low-grade metamorphic or metasomatic events, at temperatures lower than 400 °C.

Infiltrations of melts (and/or fluids) in mantle rocks are witnessed by the presence of glass-bearing pockets in peridotite xenoliths brought to the surface by alkaline volcanism. Several glass-bearing pockets found around spinels corroded at different degrees were investigated for their chemical compositions, including the Fe 3+ /∑Fe ratios, in two xenolith samples by electron probe microanalysis. The dissolution/recrystallization of spinels enriches the melt in alumina. We show that the spinel-derived Al 3+ ions could have been accommodated to the melt network first as network-modifiers. Then Al 3+ ions were network-formers using K + ions, extracted from the aqueous fluid upon melt dehydration, as stabilizers within the tetrahedral site. The transfer of K + from the aqueous fluid to the melt network is counterbalanced by an inverse transfer of CaO molecules that form crystalline phases exsolved upon eruption. The evolution of the Al content clearly shows that an increasing fraction of the spinel-derived alumina molecules was exsolved as the melt dehydration proceeded. Spinel corrosion could also be at the origin of melt oxidation through dehydrogenation reactions resulting in the formation of Al 3+ and Fe 3+ anionic complexes within the melt network. This study shows: (1) how the structure of the percolating melt is modified by the accommodation of chemical elements produced by the dissolution of minerals, and (2) how this process could modify the oxidation state of the melt.

Elastic plastic self-consistent (EPSC) simulations are used to model synchrotron X‑ray diffraction observations from deformation experiments on fayalite olivine using the deformation DIA apparatus. Consistent with results from other in situ diffraction studies of monomineralic polycrystals, the results show substantial variations in stress levels among grain populations. Rather than averaging the lattice reflection stresses or choosing a single reflection to determine the macroscopic stress supported by the specimen, an EPSC simulation is used to forward model diffraction data and determine a macroscopic stress that is consistent with lattice strains of all measured diffraction lines. The EPSC simulation presented here includes kink band formation among the plastic deformation mechanisms in the simulation. The inclusion of kink band formation is critical to the success of the models. This study demonstrates the importance of kink band formation as an accommodation mechanism during plastic deformation of olivine as well as the utility of using EPSC models to interpret diffraction from in situ deformation experiments.

Primary black thick-prismatic Al-rich schorl to rare fluor-schorl (TurP1), locally overgrown by brownish-green Li-rich fluor-schorl to fluor-elbaite (TurP2) from the Kracovice pegmatite (mixed NYF+LCT signature), was partly replaced by secondary Li-rich fluor-schorl to fluor-elbaite (TurS) plus the assemblage REE-bearing epidote-group mineral + chamosite. Primary Al-rich schorl (TurP1) shows high and variable contents of Sc (33-364 ppm) and Y+REE (40-458 ppm) with steep, LREEenriched REE pattern. Overgrowing (TurP2) and replacing (TurS) Li-rich fluor-schorl to fluor-elbaite is typically depleted in Sc (21-60 ppm) and Y+REE (3-47 ppm) with well-developed tetrad effect in the first (La-Nd) and the second (Sm-Gd) tetrads. Scandium- and REE-rich black tourmaline (TurP1) crystallized earlier from the melt, whereas crystallization of primary Li-rich fluor-schorl to fluor-elbaite (TurP2) most likely took place during late magmatic to early hydrothermal conditions. Both the secondary Li-rich fluor-schorl to fluor-elbaite (TurS) and the unusual assemblage of REE-bearing epidotegroup mineral + chamosite are likely coeval products of subsolidus reactions of the magmatic Al-rich schorl (TurP1) with evolved REE-poor, Li,F-rich, alkaline pegmatite-derived fluids. Well-crystalline REE-bearing epidote-group mineral (Y+REE = 0.42-0.60 apfu) confirmed by Raman spectroscopy has a steep, LREE-rich chondrite-normalized REE pattern with significant negative Eu anomaly and shows variable and high contents of Sc (≤3.3 wt% Sc 2 O 3 ) and Sn (≤1.0 wt% SnO 2 ). Substitution ScAl -1 and minor vacancy in the octahedral sites are suggested in the REE-bearing epidote-group mineral.

Apatite fission-track length and etch figure data are powerful tools for obtaining thermal history information, but both require human analysts making manual measurements and reproducibility is not assured. We report the results of an inter-laboratory study designed to clarify areas of congruence and divergence for these measurements and provide a basis for evaluating best practices to enhance intercompatibility of data sets. Four samples of megacrystic apatite from Durango, Mexico, with induced tracks, one unnannealed and three thermally annealed by varying amounts, were distributed internationally. In all, 55 analysts in 30 laboratory groups participated in the experiment. Relative mean track lengths among the samples were consistent across all analysts, but measurements for each sample showed scatter among labs and analysts considerably in excess of statistical expectation. Normalizing measurements of annealed samples using the unannealed sample improved consistency, as did normalizing for track angle using c-axis projection. Etch figure data also showed variability beyond statistical expectation, and consistency was improved by normalizing. Based on these data we recommend rigorous analyst training for length and etch figure measurement that includes measurement of standards, and that each analyst’s data on unknowns be normalized by that analyst’s own measurements on standards when using thermal history inverse modeling as part of the interpretation process.

The origin of yellow cathodoluminescence (CL) in quartz has been investigated by a combination of CL microscopy and spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and spatially resolved trace-element analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The study shows that the appearance of a ~570 nm (2.17 eV) emission band can be attributed to high oxygen deficiency and local structural disorder in quartz. A proposed luminescence center model implies self-trapped exciton (STE) emission from localized amorphized regions in quartz. Although the high-intensity emission at 570 nm is in general consistent with high concentrations of E′ 1 defects detected by EPR spectroscopy, CL studies with different electron beam parameters and annealing experiments up to 600 °C show a temperature and irradiation dependence of the luminescence related defects excluding the role of E′ 1 centers as direct luminescence activators for the 570 nm emission. The evaluation of geochemical data shows that quartz with yellow CL occurs in low-temperature hydrothermal environment (mostly <250 °C) and is related to fast crystallization in an environment with oxygen deficiency.

The presence of water in the Earth’s deep mantle is an issue of increasing interest in the field of highpressure mineralogy. An important task for further advancing research in the field is to create homogeneous single crystals of candidate deep-mantle water-bearing minerals of 1 mm or larger in size, which is required for applying them for the time-of-flight (TOF) single-crystal Laue diffraction method with a third-generation neutron instrument. In this study, we perform several experiments to demonstrate an improved methodology for growing hydrous crystals of such large sizes at relevant transition zone and lower-mantle conditions via very slow cooling over a maximum period of 1 day. Successfully synthesized crystals using this methodology include dense hydrous magnesium silicate (DHMS) phase E, hydrous wadsleyite, hydrous ringwoodite, and bridgmanite (silicate perovskite). It is also demonstrated that these hydrous crystals can be grown from deuterium enriched starting materials in addition to those having a natural hydrogen isotope ratio. Magnitudes of chemical and crystallographic heterogeneities of the product crystals were characterized by comprehensive analysis of X‑ray precession photography, single-crystal X‑ray diffraction (SCXRD), field-emission scanning electron microscope (FE-SEM), electron probe microanalyzer (EPMA), secondary ion mass spectroscopy (SIMS), powder X‑ray diffraction (PXRD), and TOF neutron powder diffraction (TOF-NPD). The product crystals were confirmed to be inclusion free and crystallographically homogeneous. Compositional and isotopic differences of major elements and hydrogen isotope abundances were lower than 1 and 3%, respectively, among intracrystals and intercrystals within each recovered sample capsule. Phase E crystals up to 600 μm in the largest dimension were grown at a constant temperature of 1100 °C kept for 3 h. Using a lattice parameter-to-temperature relation of phase E, the thermal gradient in the sample capsules for the phase E synthesis has been evaluated to be 20 °C/mm. Hydrous wadsleyite crystals up to 1100 μm in the largest dimension were grown at 1390 °C with a temperature reduction of 70 °C during heating for 10 h. Hydrous ringwoodite crystals up to 1000 μm in the largest dimension were grown at around 1400 °C with a temperature reduction of 110 °C during heating for 12 h. Bridgmanite crystals up to 600 μm in the largest dimension were grown at 1700 °C with a temperature reduction of 30 °C during heating for 12 h. A TOF single-crystal diffraction instrument has been successfully used for analyzing one of the hydrous wadsleyite crystals, which demonstrated that single crystals appropriate for their expected usage are created using the method proposed in the present study.

A mineral intermediate between sillimanite and mullite, tentatively designated as “sillimullite,” was studied by electron microprobe analyses and single-crystal X‑ray diffraction methods. The chemical compositions derived from the microprobe results and the crystal-structure refinement are Al 7.84 Fe 0.18 Ti 0.03 Mg 0.03 Si 3.92 O 19.96 and Al 8.28 Fe 0.20 Si 3.52 O 19.76 (Fe is Fe 3+ ) corresponding to x-values of 0.02 and 0.12, respectively, in the solid-solution series Al 8+4x Si 4-4x O 20-2x assigning Fe 3+ , Ti, and Mg to the Al site. The composition derived from microprobe analysis is very close to a stoichiometric sillimanite (with Fe 3+ ,Ti, and Mg assigned to Al sites), while the composition derived from diffraction data is midway between sillimanite and Si-rich mullites. The discrepancy is assumed to be caused by the occurrence of amorphous nano-sized SiO 2 inclusions in the aluminosilicate phase not affecting the diffraction data but detected in the microprobe analysis. “Sillimullite” crystallizes in the orthorhombic space group Pnam with a = 7.5127(4), b = 7.6823(4), c = 5.785(3) Å, V = 333.88(4) Å 3 , Z = 1. It has a complete Si/Al ordering at tetrahedral sites like sillimanite but with neighboring double chains of SiO 4 and AlO 4 tetrahedra being offset by ½ unit cell parallel to c relative to each other causing the change of the space-group setting from Pbnm (sillimanite) to Pnam. Difference Fourier calculations and refinements with anisotropic displacement parameters revealed the formation of oxygen vacancies and triclusters as known in the crystal structures of mullite. Final refinements converged at R1 = 5.9% for 1024 unique reflections with F o > 4s(F o ). Fe was found to reside predominantly in the octahedral site and with minor amounts in one of the T* sites. Mg and Ti were not considered in the refinements. The crystal studied here is considered to represent a new mineral intermediate between sillimanite and mullite, named “sillimullite.”

Yusupovite, ideally Na 2 Zr(Si 6 O 15 )(H 2 O) 3 , is a new silicate mineral from the Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz river, area of the joint Turkestansky, Zeravshansky, and Alaisky ridges, Tajikistan. Yusupovite was found in a pegmatite composed mainly of reedmergnerite, aegirine, microcline, and polylithionite. It occurs as prismatic grains about 2 mm in size embedded in reedmergnerite; associated minerals are quartz, pectolite, zeravshanite, mendeleevite-(Ce), fluorite, leucosphenite, a pyrochlore-group mineral, neptunite, telyushenkoite, moskvinite-(Y), and shibkovite. Yusupovite is colorless, transparent with a white streak, has a vitreous luster, and does not fluoresce under ultraviolet light. Cleavage is perfect on {110}, parting was not observed. Mohs hardness is 5. Yusupovite is brittle with a splintery fracture. The measured and calculated densities are 2.69(2) and 2.713 g/cm 3 , respectively. Yusupovite is optically biaxial (+) with refractive indices (λ = 589 nm) α = 1.563(2), β = 1.565(2), γ = 1.577(2); 2V meas = 42(3)°, 2V calc = 45°, strong dispersion: r > v. Yusupovite is monoclinic, C2/m, a = 14.5975(4), b = 14.1100(4), c = 14.4394(4) Å, β = 90.0399(4)°, V = 2974.1(3) Å 3 . The six strongest reflections in the X‑ray powder diffraction data [d (Å), I, (hkl)] are 7.05, 100, (020); 3.24, 96, (420); 3.10, 69, (241, 2̅41); 5.13, 53, (202, 2̅02); 6.51, 42, (201, 2̅01); 3.17, 34, (042). The chemical composition (electron microprobe) is: Nb 2 O 5 0.39, SiO 2 58.84, ZrO 2 16.55, HfO 2 0.30, FeO 0.01, Y 2 O 3 3.05, Cs 2 O 2.58, K 2 O 0.95, Na 2 O 8.91, H 2 O calc 7.40, total 98.98 wt%, with H 2 O calculated from structure refinement. The empirical formula (based on 17.5 O apfu) is (Na 1.76 K 0.12 Cs 0.11 ) ∑1.99 (Zr 0.82 Y 0.17 Nb 0.02 Hf 0.01 ) ∑1.02 (Si 6.01 O 14.98 )(H 2 O) 2.52 , Z = 8. The crystal structure of yusupovite was refined to R1 = 3.46% based on 4428 observed reflections. In the crystal structure, there are six Si sites occupied by Si, two M sites occupied mainly by Zr with minor Y and Hf. Si tetrahedra form an epididymite Si 6 O 15 ribbon along [010]. Epididymite ribbons and Zr-dominant M octahedra share common vertices to form a heteropolyhedral Si-Zr-O framework. There are six interstitial sites partly occupied by alkali cations Na, K, and Cs. The three [7]-coordinated Na sites are occupied by Na at 95, 84, and 78%. The three A sites are occupied by K and Cs at 12, 18, and 16%. There are 10 W sites occupied by H 2 O groups at 18-84%. Due to (K,Cs), Na and H 2 O disorder, the symmetry of yusupovite decreases from orthorhombic, space group Pbcm (elpidite), to monoclinic, space group C2/m, and the b unit-cell parameter of yusupovite is doubled compared to the corresponding cell parameter in elpidite, b yus = 2a elp . Yusupovite, ideally Na 2 Zr(Si 6 O 15 )(H 2 O) 3 , is a dimorph of elpidite, Na 2 Zr(Si 6 O 15 )(H 2 O) 3 .

Naturally occurring mackinawite (tetragonal FeS) with incorporated transition metals is an important precursor to the formation of metal sulfides in ore deposits, but experimental results have not been sufficient to establish clear trends in the structure and stability of the transition-metal-enriched mineral. Using density functional theory with dispersion corrections, we report the first systematic examination of the relationship between composition and structure for FeS incorporating bivalent transition metals. Our method was validated by successful calculations of the structures of FeS, FeSe, FeSe 1-x S x , Fe 1-x Me x Se (Me = Co, Ni, Cu), and FeNi x Te. Two classes of transition-metal-incorporated FeS structures then were investigated: Fe 1-x Me x S (metal-substituted FeS) and FeMe x S (FeS intercalated by a metal at either a tetrahedral or square-pyramidal interstitial site), where Me = Co, Ni, and Cu, and x ≤ 0.25. We find that incorporated transition metals can both increase and decrease lattice parameters, depending on the metal and how it is incorporated into the FeS structure. As the mole fraction of substituting metal increases, the FeS unit-cell volume decreases for Co, is nearly constant for Ni, but increases for Cu. Metal substitution changes the c lattice parameter, which is sensitive to interactions between the mackinawite sheets, as much as it does the a and b lattice parameters. Upon intercalation, the unit-cell volume and c parameter increase but the a and b parameters decrease. Experimental structural data are consistent with our results for metal-substituted FeS. We determined the thermodynamic stability of metal-incorporated FeS by computing the free energy involved in the metal incorporation reactions as a function of chemical potential of sulfur. The thermodynamic results lead to the general conclusions that metal incorporation into mackinawite most likely occurs via substitution, which may be important to influence phase transformation pathways of mackinawite.

Plastic deformation of diamond has long been associated with the generation of color, specifically brown and pink. Extensive previous optical and spectroscopic characterization of natural pink Type I (nitrogen containing) diamonds has revealed two clear groupings, with distinct geographical origins. Group 1 pinks, which have low concentrations of nitrogen and are relatively highly aggregated (IaA ≤ B), have only been found in the Argyle lamproite pipe (Australia) and Santa Elena alluvial deposits (Venezuela). Group 2 pinks, which have much higher nitrogen concentrations and exhibit low levels of aggregation, have been found in deposits from southern Africa, Canada, and Russia. Pink color is intimately associated with deformation lamellae on the {111} crystal planes, and understanding their formation and structure has been a priority with respect to defining the source of this gemologically valuable color center. In group 2 pinks, these {111} lamellae have been characterized as deformation microtwins by both transmission electron microscopy and X‑ray diffraction. Subsequently the {111} lamellae in group 1 pinks have been assumed to also be deformation microtwins. In this paper we report electron backscatter diffraction (EBSD) studies of three brown and six pink naturally deformed diamonds with varying nitrogen concentrations and aggregation states. The results show that there are no deformation microtwins in the group 1 pink or brown diamonds. The study also highlights the usefulness of orientation contrast imaging as a simple and rapid method for determining the presence of microtwins. Our results suggest that the color in the group 1 pink diamonds is not directly related to the presence of deformation twins. However, we propose that twins may have been present but subsequently removed by de-twinning, a process that utilizes the same Shockley partial dislocations involved in the original twinning event. Therefore, it may be the process of twinning (and de-twinning) that creates the defect responsible for pink color, as opposed to the actual structure of microtwins themselves. In addition, a large laboratory data set of pink diamond analyses reveals the occurrence of group 1 pink diamonds in the Namibian marine (secondary) deposits. This would appear to suggest an additional source of group 1 pink diamonds in southern Africa, but the antiquity of these diamonds means that a common source on the former Pangaea supercontinent cannot be ruled out.

The influence of three-dimensional defects on the morphology of diamond dissolution in watercontaining carbonate melts was studied at a pressure of 5.7 GPa and a temperature of 1300 °C, using a BARS multi-anvil apparatus. Experiments on stage-by-stage dissolution were performed for four blocky synthetic diamond crystals. Initial crystals had polycentric structure of the faces, strong strains, block structure, numerous microtwins, and microinclusions. It has been established that the main relief features of partly dissolved diamond crystals are shield-shaped laminae and negative trigons on remnants of {111} faces, deep etch channels, rectilinear steps on microtwins, and hillocks on rounded surfaces. The produced dissolution forms have shagreen or block-type rounded surfaces. The main element of the relief are hillocks. Their shape is controlled by the orientation of the surface on which they are localized. For natural rounded diamonds it is found that the dissolution drop-like hillocks on the surfaces are also related to strong lattice strains occurring in the crystals. The established relation between the dissolution hillocks and diamond deformation can be used for the reconstruction of the post-growth history of natural diamonds as well as for the preliminary evaluation of their quality

Granitic lunar samples largely consist of granophyric intergrowths of silica and K-feldspar. The identification of the silica polymorph present in the granophyre can clarify the petrogenesis of the lunar granites. The presence of tridymite or cristobalite would indicate rapid crystallization at high temperature. Quartz would indicate crystallization at low temperature or perhaps intrusive, slow crystallization, allowing for the orderly transformation from high-temperature silica polymorphs (tridymite or cristobalite). We identify the silica polymorphs present in four granitic lunar samples from the Apollo 12 regolith using laser Raman spectroscopy. Typically, lunar silica occurs with a hackle fracture pattern. We did an initial density calculation on the hackle fracture pattern of quartz and determined that the volume of quartz and fracture space is consistent with a molar volume contraction from tridymite or cristobalite, both of which are less dense than quartz. Moreover, we analyzed the silica in the granitic fragments from Apollo 12 by electron-probe microanalysis and found it contains up to 0.7 wt% TiO 2 , consistent with initial formation as the high-temperature silica polymorphs, which have more open crystal structures that can more readily accommodate cations other than Si. The silica in Apollo 12 granitic samples crystallized rapidly as tridymite or cristobalite, consistent with extrusive volcanism. The silica then inverted to quartz at a later time, causing it to contract and fracture. A hackle fracture pattern is common in silica occurring in extrusive lunar lithologies (e.g., mare basalt). The extrusive nature of these granitic samples makes them excellent candidates to be similar to the rocks that compose positive relief silicic features such as the Gruithuisen Domes.

The Callovian-Oxfordian (COx) clay formation in the Paris Basin (France) has been the target of many studies investigating the feasibility of deep nuclear waste disposal in a reduced clay formation. To determine the mobility of radionuclides in the host rock formation, modeling of the porewater chemistry, particularly iron solute concentrations, is necessary. Notably, this study aims to understand the supersaturation of Fe(III) oxyhydroxides given by models. Fe(III) oxyhydroxides have been identified magnetically in unpreserved Callovian-Oxfordian samples. In this study, a set of magnetic measurements are used to detect the Fe-bearing magnetic minerals present in the COx clay formation. A core sample from the borehole FOR1118, preserved from air since its collection, is the target of this study. The magnetic measurements performed show that magnetite and goethite are the main magnetic minerals (<0.2%), together with probable greigite, and occur in low concentrations. Goethite occurs as nanoparticles dispersed in the clayey matrix, and not enclosed in other minerals or in organic matter. It is unlikely that the goethite is an alteration by-product, as particular care was undertaken. This finding resolves the discrepancies between observations and previous modeling results.

The R fluorescence lines of rubies that contain 0.022, 0.068, 0.211, 0.279, 0.556, 1.221, and 1.676 wt% of Cr 2 O 3 were measured at temperatures of 100-600 K and at atmospheric pressure. The R 1 line wavenumbers of all of the ruby samples shifted linearly as the temperature increased from 298 to 600 K at atmospheric pressure, and the temperature dependence increased from -0.157 ± 0.001 cm -1 /K to -0.149 ± 0.001 cm -1 /K as the Cr 2 O 3 content in the rubies increased from 0.022 to 1.676 wt%, which suggests a significant dependence on Cr 3+ concentration. At room temperature and atmospheric pressure, the full-width at half maximum (FWHM) of the peak height of the R lines also appears to be linearly related to the Cr 3+ concentration. The relative intensity ratios of the R 2 to R 1 lines (I 2 /I 1 ) of ruby samples with different Cr 3+ concentrations show several non-linear variations with temperature from 100 to 600 K, and the maximum values, (I 2 /I 1 ) max , occur near room temperature. The effect of Cr 3+ doping on the temperature dependence of the R line wavenumbers should be considered when rubies are used to calibrate the pressure or temperature in high-pressure and high-temperature experiments.

Synchrotron X‑ray powder diffraction experiments have been performed on dehydrated Csexchanged natrolite to systematically investigate successive transitions under high pressures and temperatures. At pressures above 0.5(1) GPa using H 2 O as a pressure-transmitting medium and after heating to 100 °C, dehydrated Cs 16 Al 16 Si 24 O 80 (deh-Cs-NAT) transforms to a hydrated phase Cs 16 Al 16 Si 24 O 80 ·16H 2 O (Cs-NAT-II), which has a ca. 13.9% larger unit-cell volume. Further compression and heating to 1.5 GPa and 145 °C results in the transformation of Cs-NAT-II to Cs 16 Al 16 Si 32 O 96 (anh-Cs-POL), a H 2 O-free pollucite-like triclinic phase with a 15.6% smaller unit-cell volume per 80 framework oxygen atoms (80O f ). At pressures and temperatures of 3.7 GPa and 180 °C, a new phase Cs 1.547 Al 1.548 Si 6.452 O 16 (Cs-HEX) with a hexacelsian framework forms, which has a ca. 1.8% smaller unit-cell volume per 80O f . This phase can be recovered after pressure release. The structure of the recovered Cs-HEX has been refined in space group P6 3 /mcm with a = 5.3731(2) Å and c = 16.6834(8) Å, and also been confirmed by HAADF-STEM real space imaging. Similar to the hexacelsian feldspar (i.e., BaAl 2 Si 2 O 8 ), Cs-HEX contains Cs + cations that act as bridges between the upper and lower layers composed of tetrahedra and are hexa-coordinated to the upper and lower 6-membered ring windows. These pressure- and temperature-induced reactions from a zeolite to a feldspar-like material are important constraints for the design of materials for Cs + immobilization in nuclear waste disposal.

In situ high-pressure X‑ray diffraction study was performed on synthetic lead feldspar with composition PbAl 2 Si 2 O 8 (PbFsp). The crystals were synthesized from the melt and thermally treated at T = 1150 °C for 12 h and at T = 1000 °C for 70 h. At room condition the unit-cell parameters are a = 8.3936(4), b = 13.0498(7), c = 14.3258(8) Å, β = 115.281(6)°, V = 1418.9(1) Å 3 ; space group: I2/c; Q od = 0.7. A single-crystal of lead feldspar was loaded in an ETH-type diamond-anvil cell and unit-cell parameters were measured at 26 different pressures up to 8.4 GPa at room T. The evolution with P of the unit-cell parameters and volume shows a strong discontinuity between 7.7 and 8.2 GPa indicating a first-order phase transition. The discontinuous character of the transition is especially noticeable in the behavior of the β angle, which decreases from 114.83° to 114.03°, and in the b parameter, which reduces from 12.746 to 12.567 Å. In the P range 0.0001-7.72 GPa, the trend shown by the axial compressibility (β a > β c > β b ) is similar to that observed in the previous HP powder diffraction study, performed on lead feldspar using high-brilliance synchrotron radiation up to 7.1 GPa. In the P range 0.0001-4.27 GPa at room T, the P-V data of the I2/c lead feldspar were fitted with a second-order Birch-Murnaghan EoS. The parameters obtained are: V 0 = 1422.2(1) Å 3 and K T0 = 76.4(9) GPa. At P > 4.27 GPa, the volume values deflect from the BM2 curve and show a volume softening, precursor of the reported HP phase transition. A volume softening was recently observed in strontium feldspar (SrFsp) above 4.2 GPa. A second crystal of PbFsp was loaded in the DAC cell and in situ high-pressure X‑ray diffraction intensities were measured at P = 0.0001, 2.4, 3.1, 5.4, 6.0, 7.2, 8.4, and 9.7 GPa. The appearance of c and d-type reflections at 8.4 GPa, the analysis of the systematic absence and the structural refinements indicate the HP first-order transformation as an I2/c-P2 1 /c phase transition. Structural results show that the main variations with compression in lead feldspar are in Pb-O bond lengths and in T-O-T bond angles, while T-O distances and O-T-O angles do not change meaningfully, indicating that the Si,Al tetrahedra behave with pressure as a rigid body. Changes observed in the compressional behavior of the structure between 3 and 5 GPa could explain the softening observed at P > 4 GPa in the volume compressibility. The results obtained in the present work allow comparing the pressures of the HP I2/c-P2 1 /c phase transition occurring in lead feldspar with those observed in alkaline-earth feldspars.

High-temperature oxide melt solution calorimetry was used to investigate energetics of a series of rare earth niobates RE 3 NbO 7 . All of investigated compounds were found to be stable in enthalpy in respect to their oxides. The enthalpy of formation from oxides becomes more exothermic as the size of the RE cation increases, a trend seen previously in other RE compounds including pyrochlores, perovskites, and phosphates. For smaller RE cations the enthalpy of exchange of RE between niobates and titanates is close to zero, whereas larger RE are energetically favored in the titanate pyrochlores. Implications of the results from the geochemical and material engineering points of view are discussed.

In many natural and anthropogenically affected environments, alteration of galena produces thermodynamically more stable secondary lead phases. These secondary minerals control the mobility of the toxic heavy metal lead in water. These textural, paragenetic, and stability relations have not been investigated in detail in the literature yet. An extensive petrographic study of 41 thin sections of weathered, zoned galena and adjacent country rock from the Schwarzwald mining area, southwest Germany, is presented. The observed textures were evaluated using PHREEQC fluid path modeling and sequences of stable secondary mineral assemblages were predicted. The most common secondary (supergene) lead minerals of interest here are cerussite, anglesite, and pyromorphite group minerals (PyGM; pyromorphite, mimetite, and vanadinite). These lead phases show a spatially well-ordered zoned texture around the preexisting/relic galena. Cerussite and anglesite commonly occur either as in situ replacement of galena and/or as euhedral crystals in cavities of former, partially dissolved galena. The PyGM are present either as crusts around the margin of the former/relic galena or are common as infiltration products into the host rock/gangue. During progressive weathering anglesite typically disappears first followed by cerussite. Finally, only the highly insoluble PyGM persist as a perimorphose. Hence, a spatially and temporally zoning texture is formed. Thermodynamic models of various fluid evolution paths using PHREEQC show the influence of temperature, pH, variable PCO2, phosphorous contents and/or different mineral reactions on the sequence of formation and stability of the secondary lead phases. Already small changes in one or more of these parameters can lead to different mineral assemblages or sequences of secondary lead minerals. Over almost the whole relevant pH range, PyGM are the most stable lead phases, precipitating at very low ion activities explaining their textural position. Whether cerussite or anglesite forms, depends mainly on the pH value of the supergene fluids, which is affected by the quite variable fluid pathways. Furthermore a solubility diagram for a typical near-surface fluid was calculated, showing that anglesite is the most soluble phase, followed by cerussite and PyGM. This again reflects the microscopic observations. As a further step, the time span for the formation of a natural millimeter-thick pyromorphite crust was evaluated using subsoil phosphorous fluxes from the literature. The calculation indicates that millimeter-thick pyromorphite crusts can be formed in few tens to about hundred years, which is in agreement with observations in the nature. In this study, a framework for predicting stable secondary lead mineral assemblages and textures by fluid path modeling is given. These models are potentially important for predicting the retention and mobilization of lead in systems around contaminated sites or natural ore deposits.

We have conducted a series of experiments to evaluate the intrinsic effects of dissolved chlorine on Fe 3+ /∑Fe and magnetite solubility in hydrous chloride-rich rhyodaciticliquids. The addition of Cl to the melt appears to have two prominent effects on iron in the melt: (1) dissolved Cl appears to perturb the magnetite-melt equilibrium, such that greater FeO total contents are required to support magnetite saturation in Cl-bearing melts than in Cl-free melts of equivalent bulk compositions; and (2) a systematic and progressive decrease of the measured Fe 3+ /∑Fe as f O₂ is increased. These two intimately related effects each have important implications for redox processes occurring in Cl-enriched arc magmas.

Rutile (TiO 2 ) is an important host phase for high field strength elements (HFSE) such as Nb in metamorphic and subduction zone environments. The observed depletion of Nb in arc rocks is often explained by the hypothesis that rutile sequesters HFSE in the subducted slab and overlying sediment, and is chemically inert with respect to aqueous fluids evolved during prograde metamorphism in the forearc to subarc environment. However, field observations of exhumed terranes, and experimental studies, indicate that HFSE may be soluble in complex aqueous fluids at high pressure (i.e., >0.5 GPa) and moderate to high temperature (i.e., >300 °C). In this study, we investigated experimentally the mobility of Nb in NaCl- and NaF-bearing aqueous fluids in equilibrium with Nb-bearing rutile at pressure-temperature conditions applicable to fluid evolution in arc environments. Niobium concentrations in aqueous fluid at rutile saturation were measured directly by using a hydrothermal diamondanvil cell (HDAC) and synchrotron X‑ray fluorescence (SXRF) at 2.1 to 6.5 GPa and 300-500 °C, and indirectly by performing mass loss experiments in a piston-cylinder (PC) apparatus at ~1 GPa and 700-800 °C. The concentration of Nb in a 10 wt% NaCl aqueous fluid increases from 6 to 11 μg/g as temperature increases from 300 to 500 °C, over a pressure range from 2.1 to 2.8 GPa, consistent with a positive temperature dependence. The concentration of Nb in a 20 wt% NaCl aqueous fluid varies from 55 to 150 μg/g at 300 to 500 °C, over a pressure range from 1.8 to 6.4 GPa; however, there is no discernible temperature or pressure dependence. The Nb concentration in a 4 wt% NaF-bearing aqueous fluid increases from 180 to 910 μg/g as temperature increases from 300 to 500 °C over the pressure range 2.1 to 6.5 GPa. The data for the F-bearing fluid indicate that the Nb content of the fluid exhibits a dependence on temperature between 300 and 500 °C at ≥2 GPa, but there is no observed dependence on pressure. Together, the data demonstrate that the hydrothermal mobility of Nb is strongly controlled by the composition of the fluid, consistent with published data for Ti. At all experimental conditions, however, the concentration of Nb in the fluid is always lower than coexisting rutile, consistent with a role for rutile in moderating the Nb budget of arc rocks.

Natural iron-bearing sodic phonolitic melts represent an extreme compositional range of the effect of the [Na/(Na+K)] ratio on the geochemical behavior of Fe in volcanic systems. Yet phonolitic melts have not been well investigated. The glasses studied here have been synthesized from liquids equilibrated over a range of oxygen fugacity conditions [log 10 (f O₂ ) from -0.68 to -11] to elucidate the role of the alkali ratio in influencing the local environment around both divalent and trivalent Fe. In this study, the Fe K-edge XAS spectra (XANES and EXAFS) have been employed, to constrain the Fe structural role (oxidation state, coordination number, bond distances) in phonolitic glasses as a function of synthesis temperature (T), [Na/(Na+K)] ratio (= 0.0, 0.25, 0.5, 0.75, 1.0) and redox state. We verify that at constant oxygen fugacity, the [Na/(Na+K)] ratio has a strong effect on the Fe 3+ / (Fe 2+ +Fe 3+ ) ratio. The results obtained are parameterized and discussed in terms of the contrasting effects of T, f O₂ , and alkali ratio.

A new method is presented for calculating the chemical formula for apatite, and any other mineral that features mixing between halogens and hydroxyl ions on monovalent anion sites, from electron microprobe data that omit H 2 O determination. It removes errors of up to 4% in stoichiometric calculations that occur for apatite when an incorrect normalization is used. The method also provides an estimate of OH content and uncertainty that can be included in chemical analysis totals.

The influence of carboxylic-functional-groups (-COOH) on the phase transformation from amorphous calcium phosphate (ACP) to octacalcium phosphate (OCP) was investigated. 11-Mercaptoundecanoic acid, a carboxylic thiol, was immobilized on gold nanoparticles via covalent bond formation. Time-resolved static light scattering measurements indicated that a structural-reconstruction-type phase transformation occurred with or without the presence of -COOH on the nanoparticles. When it dispersed in calcium phosphate solutions, these nanoparticles inhibited the phase transformation dynamics and also changed the reaction path, forming HPO 4 -OH-layer-deficient OCP at pH 6.5 an intermediate phase, which did not show the typical OCP X‑ray diffraction (XRD) peak at 2θ = 4.7°. This phase was not observed in the reference solution containing gold nanoparticles without bound -COOH. The HPO 4 -OH-layer-deficient OCP transformed to conventional OCP gradually, as revealed by XRD, nuclear magnetic resonance, and Raman analyses. Thus, the immobilized -COOH appeared to behave as a negative catalyst, resulting in the formation of the intermediate phase. Such a mechanism partially clarifies complex biomineralization processes, for example teeth enamel and dentin formation, in vivo.

The crystal structure and chemical composition of a crystal of Mg(Mg,Cr,Si) 2 O 4 post-spinel phase synthesized in the model system MgCr 2 O 4 -Mg 2 SiO 4 at 16 GPa and 1600 °C have been investigated. The compound was found to crystallize with a distorted orthorhombic calcium-titanate (CaTi 2 O 4 ) structure type, space group Cmc2 1 , with lattice parameters a = 2.8482(1), b = 9.4592(5), c = 9.6353(5) Å, V = 259.59(1) Å 3 , and Z = 4. The structure was refined to R 1 = 0.018 using 345 independent reflections. The loss of the inversion center is due to the ordering of cations at the octahedral sites: Cr is mainly hosted at the M1 site, whereas Si at the M2 site. Such an ordered distribution induces a distortion thus provoking a change in coordination of Mg, which becomes sevenfold-coordinated instead of the usual eightfold coordination observed in post-spinel phases. Electron microprobe analysis gave the Mg[(Cr 0.792 Mg 0.208 ) (Si 0.603 Mg 0.397 )]O 4 stoichiometry for the studied phase. The successful synthesis of this phase can provide new constraints on thermobarometry of wadsleyite/ringwoodite-bearing assemblages.

The crystal structure of the two dense hydrous magnesium silicates Phase D, MgSi 2 H 2 O 6 , and Phase H, MgSiH 2 O 4 , synthesized at 45 GPa and 1000 °C and coexisting in the same micrometer-sized grain, was investigated by single-crystal X‑ray diffraction to study the preferential partition of Al between the two structures. In agreement with the literature, Phase D was found to be trigonal, space group P3̅1m, with lattice parameters a = 4.752(2), c = 4.314(2) Å, V = 84.37(6) Å 3 (R 1 = 0.020), and Phase H was found to be orthorhombic, space group Pnnm, with lattice parameters a = 4.730(2), b = 4.324(2), c = 2.843(2) Å, V = 58.15(5) Å 3 (R 1 = 0.024). The estimated proportion (vol%) of the two phases from the refinement is 27(2) PhD - 73 PhH . The analysis of the geometric details of the two structures shows that Phase D hosts almost all the Al available, whereas Phase H is nearly identical to pure MgSiH 2 O 4 . Overexposed electron-microprobe X‑ray maps of the same grain used for the X‑ray diffraction study together with WDS spots on the two phases confirmed the structural results. Thus, our results suggest that when Phase D and Phase H coexist, Al is strongly partitioned into Phase D at the expense of coexisting Phase H. At pressure above ~50 GPa, where Phase D is no longer stable, Phase H is able to incorporate the high aluminum contents present in hydrous peridotitic compositions in the deep lower mantle and be stabilized at the expense of Phase D and magnesium silicate perovskite.

We have studied the speciation of carbon monoxide in both Fe-bearing and Fe-free basaltic glasses using Raman, FTIR, and Mössbauer spectroscopy. We show that a band at 2110 cm -1 in the Raman spectrum and another band at 2210 cm -1 in the FTIR spectrum occur both in the Fe-bearing and Fe-free samples, implying that they cannot be due to any Fe-bearing species. This observation is consistent with 57 Fe Mössbauer spectra, which do not show any evidence for Fe species with zero isomer shift, as expected for carbonyls. Thermodynamic calculations show that iron carbonyl in basaltic melts under crustal and upper mantle conditions may only be a trace species. Rather than being due to distinct chemical species, the range of vibrational frequencies observed for carbon monoxide in silicate glasses appears to be due to rather subtle interactions of the CO molecule with the matrix. Similar effects are known from the extensive literature on carbon monoxide adsorption on oxides and other surfaces. In the melt at high temperature, there is likely little interaction of the CO molecule with the silicate matrix and solubility may be largely controlled by pressure, temperature, and the overall polymerization or ionic porosity of the melt.

Using transmission electron microscopy we show that planar deformation lamellae occur within quartz in the substrate of a rock fulgurite, i.e., a lightning-derived glass. These lamellae exist only in a narrow zone adjacent to the quartz/fulgurite boundary and are comparable to planar deformation features (“shock lamellae”) caused by hypervelocity impacts of extra-terrestrial objects. Our observations strongly suggest that the lamellae described here have been formed as a result of the fulgurite-producing lightning strike. This event must have generated a transient pressure pulse, whose magnitude, however, is uncertain at this stage.