Volume 94, Issue 7

Diffraction methods indicate clearly that there are two crystallographic Al sites in kaolinite with different site symmetry. Many unsuccessful attempts have been made to resolve the two different Al sites in kaolinite by magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy since the early 1980s. This study attempts to resolve these sites, derive accurate quadrupolar coupling parameters at the two sites, and explain the reasons for the lack of separation by combining NMR spectroscopy at various fields with ab initio quantum modeling. At a high field such as 21.06 T, large chemical shift anisotropy and dipolar effects can overwhelm the quadrupolar interaction effects for sites with relatively small Cq values such as the two Al sites in kaolinite. The spectra will then display featureless lineshapes lacking the typical quadrupolar interaction characteristics. At lower fields, such as 4.68 T, the quadrupolar interaction effects become dominant, but due to the similarity of the two Al environments in kaolinite, as well as broadening by residual dipole-dipole and chemical shift anisotropy, the 27 Al MAS NMR peaks still could not be separated. To resolve the two different Al sites spectroscopically, 27 Al MAS NMR experiments at multiple magnetic fields, satellite transition NMR, and multiple-quantum MAS techniques have been utilized. Although these NMR experiments failed to resolve the two Al sites, the spectra have been interpreted with the aid of theoretical ab initio quantum mechanical modeling using full potential linearized augmented plane wave (FP-LAPW) model and the CASTEP software program. Average values of Cq, η, and δ iso for the two Al sites were constrained to be 2.6 MHz, 0.75 and 6.25 ppm with high confidence.

High-pressure and -temperature multianvil experiments were performed to test the effect of varying oxygen fugacity on the olivine to wadsleyite transformation. Two capsules, containing samples of (FeMg) 2 SiO 4 , were placed in each experiment; the first buffered the oxygen fugacity with an assemblage of Re and ReO 2 . whereas the second ensured the lowest possible ferric iron concentra- tion through the presence of excess Fe metal. Measurements of coexisting olivine, wadsleyite. and ringwoodite compositions from the Fe metal saturated experiments were used to accurately determine the pressure in each experiment using established phase relations. Under the more oxidizing conditions of the Re-ReO 2 buffer, the stability field of wadsleyite was found to expand with respect to both the olivine and ringwoodite stability fields. Mössbauer spectroscopy measurements reveal Fe 3+ /∑Fe ratios for wadsleyite buffered by Re-ReO: of 0.1-0.25. while olivine appears to be FeJ"-free. A thermodynamic model that employs the wadsleyite end-members (Fe 3+ 5/3 □ 1/3 )Fe 3+ O 4 -Fe 2 SiO 4 -Mg 2 SiO 4 is used to examine the effect of varying bulk mantle Fe 3+ /∑Fe ratio on the depth and depth interval of the 410 km seismic discontinuity. Fe 3+ /SFe ratios in the range 0.02-0.12 would cause the depth interval or thickness of the 410 km discontinuity to increase from -8 to 15 km but would haw very little effect on the seismically observable absolute depth. Very large bulk mantle Fe 3+ /∑Fe ratios (>0.2), unrepresented in recovered mantle samples, would be required to explain recent seismic observations that the depth interval of the 410 km may be >20 km beneath certain regions. Such observations are more likely to be explained by moderate local enrichments in both ferric iron and H;0 in the mantle, most likely as a result of slab interaction.

Spectroscopic measurements have been made of two suites of olivine minerals synthesized under slightly different conditions in 5-10 mol% increments across the solid solution from forsterite to fayalite. Here, we present Mössbauer results for the entire Fe-Mg olivine suite, as well as the results for only the fayalite end-member as an introduction to our team’s other diverse spectral-analysis techniques and data that will be presented in forthcoming papers. Experimental methods used to synthesize both suites of samples are discussed here in detail, along with specifics of the analytical techniques used to study them. Electron microprobe data and Mössbauer spectra acquired at 293 K across the solid solution are presented first to characterize and address the presence of impurities in the broad suite of samples that may affect other spectroscopic methods. We then focus specifically on the fayalite end-member to illustrate its properties using multiple techniques. Fayalite is an especially important phase for different types of spectroscopy because, by definition, it contains an equal distribution of Fe 2+ cations between the M1 and M2 octahedral sites. Thus, features associated with each of the two sites must represent equal numbers of Fe 2+ cations, removing uncertainties associated with assumptions about order/disorder of Fe 2+ and other cations. Mössbauer, Raman, thermal emission, attenuated total reflectance (ATR), specular reflectance, and visible to mid-infrared total reflectance studies are presented for fayalite. These include calculation of mid-infrared optical constants (n and k) and fundamental Mössbauer parameters: intrinsic isomer shift (δI), Mössbauer temperature (θM), and recoil-free fraction (f). Data from the different techniques are described and related, demonstrating the importance of multi-wavelength data to provide a complete characterization and understanding of the spectroscopic features in fayalite.

Single-crystal X-ray diffraction has been used to measure the thermal expansion coefficients of forsterite, wadsleyite, ringwoodite, and their hydrous forms at ambient pressure, from temperatures as low as 133 K to as high as 919 K. Second-order polynomial fitting to ln(V/V 0 ) vs. T was applied to derive the expansion coefficients in the form of α = a 1 × T + a 0 . The single crystal of anhydrous wadsleyite persisted up to 859 K. Hydrous forsterite was observed to dehydrate at 919 K, whereas hydrous wadsleyite started to dehydrate at 655 K. The crystal of ringwoodite with 0.20 wt% broke down at 911 K, and the two ringwoodite samples with 0.74 and 2.4 wt% H 2 O, were observed to break down with an irreversible unit-cell expansion at 808 and 606 K, respectively. From room temperature to high temperatures in this study, the mean thermal volume expansion coefficients are 36.4(5) and 38.1(9) × 10 -6 K -1 , respectively, for anhydrous and hydrous forsterite; 28.5(5) and 35.8(8) × 10 -6 K -1 , respectively, for the anhydrous and hydrous wadsleyite; 30.6(9), 35.2(15), and 34.9(7) × 10-6 K -1 for the samples of ringwoodite with 0.2, 0.74, and 2.4 wt% H 2 O, respectively. Thus, forsterite, wadsleyite, and ringwoodite all have larger thermal expansion coefficients in their hydrous forms than in their anhydrous forms.

We present a detailed 29 Si NMR spectroscopic study of isotopically enriched samples of forsterite and of anhydrous and hydrous wadsleyite and ringwoodite (α, β, and γ phases of Mg 2 SiO 4 ), which complement previous extensive studies of these minerals by XRD and vibrational spectroscopy. VISi is not detected in any of the phases at levels of about 0.1 to 0.5%. When coupled with recent theoretical calculations on ringwoodite, this suggests the possibility of re-ordering of high-temperature octahedral-tetrahedral disorder during cooling. Cross-polarization ( 29 Si{ 1 H} CPMAS) NMR supports the protonation of O1 oxygen atoms in hydrous wadsleyite without formation of significant amounts of Si-OH groups. In contrast, new NMR peaks appear in hydrous ringwoodite that cross-polarize very rapidly, indicating very short Si-H distances and the presence of Si-OH, as expected from models in which much of the H + substitutes into Mg 2+ vacancies. Static NMR spectra provide new constraints on chemical shift anisotropies in wadsleyite and are fully consistent with the cubic structure of ringwoodite. Spin-lattice relaxation in all phases is much better fitted by a stretched exponential function than with a more conventional “T 1 ” exponential, as expected when relaxation is dominated by paramagnetic impurities. However, the effects of paramagnetic impurity on ion contents on relaxation, and on the formation of newly observed minor peaks that may result from “pseudo-contact shifts,” appear to depend on mineral structure, and will require considerable future study to understand in detail.

The compressibility, phase stability, and vibrational properties of coffinite (USiO 4 ) were studied by in situ X-ray diffraction and infrared (IR) measurements at high pressures. An irreversible phase transition from the zircon-type to scheelite-type structure was found to occur at 14-17 GPa. Accompanying the structural transition, partial amorphization was also evident in the XRD analysis. The predicted transition pressure calculated by density functional theory is in good agreement with the experimental results. IR spectra also suggest that water is incorporated into the coffinite structure, and a pressure-induced electron transfer (U 4+ → U 5+ ) may also occur.

Fe-Mg partitioning between perovskite and ferropericlase in the MgO-FeO-SiO 2 system has been studied up to about 100 GPa at around 2000 K using a laser-heated diamond anvil cell (LHDAC). The compositions of both phases were determined by using analytical transmission electron microscopy (ATEM) on the recovered samples. Present results reveal that the Fe-Mg apparent partition coefficient between perovskite and ferropericlase [K D Pv/Fp = (X Fe Pv X Mg Fp )/(X Mg Pv X Fe Fp )] decreases with increasing pressure for a constant FeO of the system, and it decreases with increasing FeO content of ferropericlase. The gradual decrease of K D Pv/Fp with increasing pressure is consistent with the spin transition in ferropericlase occurring in the broad pressure range from 50 to 100 GPa at around 2000 K.

The oxygen-isotope composition of the Earth’s upper mantle is an important reference for understanding mantle and crust geochemical cycles. Olivine is the most commonly used mineral for determining the influence of crustal processes on the oxygen-isotope ratio (δ 18 O) of primitive rocks, however it is an uncommon mineral in continental crust and readily alters at or near Earth’s surface. Here we report the first measurements of oxygen-isotope ratios in zircon from oceanic crust exposed at a mid-ocean ridge. Measurements of δ 18 O and trace elements were made by ion microprobe on zircon in polished rock chips of gabbro and veins in serpentinized peridotite drilled from the Mid-Atlantic Ridge. The zircon grains contain both oscillatory and sector growth zoning, features characteristic of magmatic zircon. Values of δ 18 O (zircon) = 5.3 ± 0.8‰ (2 st. dev., n = 68) for the population are consistent with the interpretation that these grains are igneous in origin and formed in high-temperature isotopic equilibrium with mantle oxygen. The δ 18 O values demonstrate that zircon in oceanic crust preserves primitive δ 18 O in spite of sub-solidus alteration of the whole rock. The fact that the primitive δ 18 O (zircon) values fall in a narrow range (5.3 ± 0.8‰) strengthens the use of oxygen isotopes in zircon as a tracer to identify processes of exchange in a wide range of modern and ancient crustal environments, including subducted oceanic crust (eclogite), and also in the oldest known pieces of Earth, >3900 million-year-old detrital zircon grains from Western Australia.

Colorless natural quartz can develop many extrinsic colors after exposure to ionizing radiation and heat due to trace elements such as aluminum, iron, hydrogen, lithium, and sodium. The infrared spectrum of colorless natural quartz is correlated to the development of these colors, because the bands between 3200 and 3600 cm -1 are related to the presence of trace elements. The colors produced by γ-ray or electron beam irradiation are caused by displacements of electrons in the quartz lattice and can be bleached by ultraviolet irradiation. Colors produced by irradiation and additional heating, however, are resistant to ultraviolet rays, probably due to Li + diffusion. The infrared spectra of colorless natural quartz crystals can be used to identify the crystals’ potential for color development by irradiation and heating. At room temperature, all natural colorless samples of alpha quartz show bands at 2499, 2600, 2677, 2771, 2935, and 3063 cm -1 . The samples that do not develop color after irradiation also show bands at 3202 and 3304 cm -1 . The samples that become grayish to black after irradiation show three additional bands at 3381, 3433, and 3483 cm -1 . This last band is related to the development of the colors greenish yellow, yellow, or brown (citrine) after irradiation and heating. The samples that become grayish olive green after irradiation and olive green after additional heating show a pair of bands at 3404 and 3510 cm -1 in addition to the former bands noted. The samples that become violet (amethyst) or green (prasiolite) after irradiation, or sky blue after irradiation plus heating show a broad band at ~3441 cm -1 and a band at 3585 cm -1 .

Five clinopyroxenes containing various amounts of six-coordinated Si (VISi) in the Na(Mg 0.5 Si 0.5 ) Si 2 O 6 (NaPx)-NaAlSi 2 O 6 (jadeite) system have been synthesized at 15 GPa and 1600 °C and their structures studied with single-crystal X-ray diffraction and Raman spectroscopy. The results show that clinopyroxenes with VISi ≤ 0.33 atoms per formula unit (apfu) possess C2/c symmetry, whereas those with VI Si ≥ 0.45 apfu crystallize with P2/n symmetry. There is an obvious discontinuity in the unit-cell parameters a, β, and V as the VI Si content increases from 0.33 to 0.45 apfu, suggesting that the C2/c-P2/n transition is first-order in character, rather than tricritical as reported for the transition from jadeite/diopside/augite to omphacite. The Mg and VI Si cations in the P2/n structure are completely ordered into two nonequivalent octahedral sites, M1 and M1(1), respectively, with M1 being appreciably more distorted than M1(1). With increasing mean <M1-O> distance, the mean tetrahedral <Si-O> distance increases, whereas the O3-O3-O3 angle of the tetrahedral chain decreases systematically, consistent with the structural variation trends found in the jadeite-diopside system. A comparison of the Raman spectra reveals that the C2/c-P2/n transition is characterized by the splitting of many Raman bands in C2/c clinopyroxenes into doublets in P2/n, and such splitting becomes more pronounced with increasing VI Si. For C2/c clinopyroxenes, all Raman bands become progressively broader with the increased substitution of (Si 4+ + Mg 2+ ) for Al 3+ . In addition, several new Raman bands, attributable to the presence of VI Si, are observed. Together with previous data, we suggest that the maximum VI Si content allowed for an Mg/Al dominated octahedral site is close to ~35%, above which VI Si and Mg/ Al are likely to be ordered into distinct sites.

Structural phase transformations of MgSiO 3 protoenstatite at high pressures are studied by atomic scale simulation techniques. Molecular-dynamics simulations and electronic-structure calculations reveal two metastable polymorphs with space groups P2 1 cn and Pbcn, respectively. They are related to protoenstatite by displacive transition mechanisms via subsequent change of the silicate chain rotations from O- to S-type. Metadynamics simulations in combination with molecular dynamics reveal possible mechanisms for the martensitic transition from protoenstatite to high-pressure clinoenstatite. Two different shear mechanisms in the (100) plane are activated during the transition. The first consists of four partial displacements in (100)[001] and (100)[010], whereas in a second step only a single shear in (100)[001] is observed.

Granitoid monazite is a potential candidate for restitic origin because of its very low dissolution rates. A biotite-garnet granite (Nízke Tatry Mountains, Slovakia) contains monazite characterized by older, BSE-bright domains irregularly replaced by BSE-dark domains. They are interpreted as the result of late-magmatic replacement by a dissolution-reprecipitation mechanism. Garnet is mostly magmatic, with peritectic cores, and the granite is thought to have formed by biotite fluid-absent melting. Xenotime-monazite and garnet-biotite thermometry yield 600-650 °C at 400 MPa, for Yrich monazite, suggesting that equilibration took place in the presence of fluid. Chemical and textural relations enable the distinction of four types of monazite, which have been dated. Type I monazite, forming grain interiors, is Th-rich and overgrown by a lower-Th type II variety. Type III monazite has the lowest U and also overgrows the type I, whereas type IV monazite has the highest U (and Y) contents. U/Pb-Th/Pb isochrons reveal that, whereas monazite types I and III are older (355 ± 7 Ma), the age corresponding to the Variscan metamorphic peak, types II and IV are ca. 10 million years younger (346 ± 3 Ma, type IV). Monazite types I-III are considered to be inherited from a metamorphic protolith, whereas type IV is interpreted to be the age of the latest magmatism. Application of LREE and Zr diffusion coefficients to monazite and zircon indicates that the accessory restite assemblage observed is consistent with a short magma residence time (<500 years) during which monazite remained mostly intact, whereas zircon was partly dissolved.

Molecular dynamics simulations using a pair-wise additive potential are implemented to investigate self-diffusion (Mg, Si, and O) and shear viscosity of liquid MgSiO 3 in the density-temperaturepressure range 2350-5300 kg/m 3 , 2500-5000 K, and 0-140 GPa, respectively. Self-diffusivity and shear viscosity are described by modified Arrhenian expressions, which feature a pressure-dependent activation volume. Activation energies for self-diffusion (Mg, Si, and O) and viscous flow are 99.6, 109.3, 97.4, and 95.3 kJ/mol, respectively; evidently oxygen mobility dominates liquid dynamics. Activation volumes for self-diffusion and shear viscosity at low (2-5 GPa) pressure are ~1 cm 3 /mol with self-diffusion decreasing and shear viscosity increasing as pressure increases although there is a small interval near zero pressure within which diffusivity increases slightly with increasing pressure. Shear viscosity increases by a factor of 75 along the 3000 K isotherm from the top of the mantle to the core-mantle boundary. Along the 3000 K isentrope relevant to terrestrial magma ocean convection, shear viscosity increases by about a factor of three. The equivalence conditions between the Stokes- Einstein and Eyring transport models are derived. The Eyring model provides information on the size of the activated complex associated with viscous flow across the range in pressures relevant to the Earth’s mantle and suggests that the number of atoms in the activated complex associated with shear flow decreases from ~8 atoms at low pressure to ~4 atoms at high pressure at 4500 K.

Incorporation of water in anhydrous synthetic beryl was studied at 500-700 °C and 50-150 MPa of confining water pressure to measure the diffusion of water molecules along the channels in a cyclosilicate. A series of polarized IR spectra series were taken with E parallel to the channel direction, which is parallel to the c-axis, along a traverse parallel to this axis. Water concentration profiles were determined from absorbance of H 2 O peaks. The IR spectra showed that the dominant diffusing species is type I water molecule, whose H-H vector is parallel to the c-axis (sharp peak at 3700 cm −1 ). No pressure dependence on water diffusivity can be recognized under these experimental conditions. The Arrhenius relation gives the activation energy of 133 ± 12 kJ/mol, with a pre-exponential factor of 10−2.6 (cm 2 /s). Diffusion of water is much faster in the beryl channels than volume diffusion in other silicates, but the activation energy and diffusion coefficient values for beryl are similar to the corresponding values previously reported for grain boundary diffusion in quartz aggregates.

The vibrational spectrum of lizardite at the Γ point has been calculated with ab initio methods, using a hybrid HF/DFT Hamiltonian (B3LYP). Apart from a few bending modes involving hydrogen motion, very good agreement has been found between calculated and experimental infrared and Raman spectra of the mineral. The anharmonic correction to the OH-stretching modes proved to be crucial for a correct evaluation of their frequencies and, on average, it amounts to a lowering of about 150 cm -1 with respect to the values computed within the harmonic approximation. LO-TO splitting effects had to be taken into account for a correct interpretation of the data obtained from infrared spectra on powder samples. The calculation can be used either to confidently identify which bands in the experimental spectra do correspond to fundamental vibrational transitions or to unequivocally assign them to specific normal modes.

The 2004-2006 eruption of Mount St. Helens produced a sequence of lava domes characterized by a 1-3 m thick outer carapace of highly brecciated and comminuted dacite fault rocks. This outer layer of fault rocks is proposed to be a physical manifestation of the “drumbeat” microseismicity, such that magma extrusion occurred via integration of rapid, co-seismic slip along small displacement (<5 mm) faults. A suite of deformation experiments performed on samples of Mount St. Helens (MSH) dacite under confining pressures of 0, 25, 50, and 75 MPa, at room temperature, and an average displacement rate of ~10-4/s were run to reproduce fault textures found in nature. The MSH dacite starting material has low porosity (7-8%), and a microcrystalline groundmass with little glass. A subsidiary set of deformation experiments on dacite samples from the 2006 Augustine eruption was run under identical experimental conditions to evaluate the effect of increased porosity (φ ~ 20-24%) on failure mechanisms. The MSH dacite samples show a progressive increase in peak strength with increasing confining pressure, are strong (peak stress at 75 MPa is 700 MPa) and failed by localized, brittle behavior, characterized by macroscopic fractures and rapid stress drops. In contrast, Augustine dacite deformed by distributed cataclastic flow and is much weaker (peak stress at 75 MPa is 220 MPa). We propose that the generation of low-porosity dacite was an important variable in promoting wholesale localized faulting and the attendant drumbeat microseismicity at Mount St. Helens. Microstructures of gouge developed experimentally at room temperature are remarkably similar to those developed at ~730 °C at MSH. Mode I microcracking, shear fracture of grains, and grain size comminution occurred in both natural and experimental fault rocks. Laser grain size particle analyses show peaks at 1.5 μm for experimental run products vs. peaks at 1.9 and 4 μm for natural MSH gouge. We conclude that because the MSH lava had solidified prior to faulting, temperature is secondary in importance in the formation of the gouge material. Based on the amount of fault displacement per microseismic event, the number of “drumbeats,” and the aggregate radial thickness (1-3 m) of the gouge, we calculate that the 3-6 m/day eruption rate allows for gouge-filled slip surfaces having thicknesses of 0.8-5 mm and strike lengths of 98-190 m per seismic event.

The crystal structure of synthetic konyaite, Na 2 Mg(SO 4 ) 2 ·5H 2 O, a = 5.7690(8), b = 23.951(3), c = 8.0460(11) Å, β = 95.425(2)°, V = 1106.8(3) Å 3 , space group P2 1 /c, Z = 4, was solved using singlecrystal X-ray diffraction. Hydrogen atom positions were determined and the structure solution was refined to R 1 = 3.31% and wR 2 = 6.28% for the 2167 measured independent reflections. Three distinct cation sites host the Mg and Na atoms in distorted octahedra and eight-coordinated polyhedra. The coordination polyhedra share edges to form compact sheets oriented perpendicular to b and linked to one another by hydrogen bonds. This results in a {010} tabular habit. A comparison of this structure is made to that of blödite [Na 2 Mg(SO 4 ) 2 ·4H 2 O], the dehydration product of konyaite. Konyaite is discussed within the context of the Na 2 O-MgO-SO 4 -H 2 O system. This study is part of ongoing investigations into the dehydration mechanisms and phase stability of this system.

Joëlbruggerite, ideally Pb 3 Zn 3 (Sb 5+ ,Te 6+ )As 2 O 13 (OH,O), is a new arsenate mineral (IMA 2008-034) and the Sb 5+ analog of dugganite, from the Black Pine mine, 14.5 km northwest of Philipsburg, Granite County, Montana. It is usually found perched on mimetite; other species that may be present include malachite, azurite, pseudomalachite, chalcocite, beudantite-corkite, duftite, dugganite, and kuksite, in milky quartz veins. Joëlbruggerite occurs as barrel-shaped or prismatic crystals up to about 50 μm across in various shades of purple. The crystals have an adamantine luster and a white streak. Mohs hardness is about 3. The fracture is irregular, and the tenacity is brittle. Joëlbruggerite crystals are uniaxial (-), with a calculated refractive index of n = 1.993, and weakly pleochroic: X = Y = gray, Z = purple; absorption: Z > X = Y. Crystals show straight extinction and are length-fast. The empirical chemical formula (mean of 5 electron microprobe analyses) calculated on the basis of 14 [O + OH] anions is Pb 3.112 (Zn 2.689 Fe 2+ 0.185 ) Σ2.874 (Sb 5+ 0.650 Te 6+ 0.451 ) Σ1.101 (As 1.551 P 0.203 Si 0.160 ) Σ1.914 O 13.335 (OH) 0.665 . Joëlbruggerite is trigonal, space group P321, a = 8.4803(17), c = 5.2334(12) Å, V = 325.94(12) Å 3 , Z = 1. The five strongest lines in the powder X-ray diffraction pattern are [dobs in Å (I) (hkl)]: 3.298 (100) (111), 3.008 (89) (021), 1.905 (39) (122, 131), 2.456 (36) (012, 121, 030), and 1.609 (30) (112, 132, 231, 140). The crystal structure was solved from single-crystal X-ray diffraction data and refined to R 1 = 0.038 on the basis of 604 unique reflections with F > 4σ(F). It is composed of heteropolyhedral sheets of edge-sharing (Sb,Te)O 6 octahedra and PbO 8 disphenoids, oriented parallel to (001). The sheets are cross-linked by AsO 4 and ZnO 4 tetrahedra, which share corners to form an interlinked, two- and threeconnected two-dimensional net parallel to (001). The mineral is named for Joël Brugger (born 1967), Swiss-Australian mineralogist, for his contributions to mineralogy.

Cathodoluminescence (CL) spectra of tridymite and cristobalite have broad peaks around 430 and 400 nm, respectively, both of which can be assigned to the [AlO 4 /M + ] 0 defect. The CL intensities of these spectral peaks in the blue region decrease with prolonged exposure to electron irradiation, similar to the short-lived luminescence observed in quartz, although quartz shows a lower decrease in CL intensity compared to these minerals. Cristobalite has a higher CL intensity reduction rate during irradiation than does tridymite. Irradiation of these minerals at low temperatures results in a more rapid decay of CL emission, whereas that of quartz shows no apparent change in the rate of CL emission at similar temperatures. Confocal micro-Raman spectroscopy of the electron irradiated surface of these minerals reveals the amorphization caused by the interaction of the electron beam with the surface layer to a depth of several micrometers. This suggests that such structural destruction diminishes the activity of CL emission centers related to the [AlO 4 /M + ] 0 defects by migration of monovalent cations associated with exchanged Al in the tetrahedral sites. Both samples present a considerable reduction of their CL intensities at higher temperature, suggesting a temperature quenching phenomenon. The activation energy in the quenching process was evaluated by a least-squares fitting of the Arrhenius plots, assuming the Mott-Seitz model. The result implies that the energy of non-radiative transition in this process might be transferred to lattice vibrations as phonons in two different manners. This might be related to different irradiation responses of the CL with a change in sample temperature.

Iron and Al precipitates play very important hydrochemical and environmental roles in aquatic environments affected by acid mine drainage. Despite their great importance, reliable characterization of these precipitates is problematic due to the high proportion of amorphous or poorly ordered mineral phases comprising these precipitates and because of their coexistence with intermediate to highly crystalline phases. To facilitate and improve the characterization of poorly ordered Fe and Al phases, a coupled differential X-ray diffraction (DXRD) and sequential extraction (SE) study was performed on a set of samples from an acid mine water passive treatment system. The results of these techniques indicate the presence of schwertmannite and goethite in the upper 5 cm of the passive treatment reactive material. Furthermore, a progressive decrease of the SO 4 2- adsorbed to the schwertmannite surface is suggested by one of the SE steps. The presence of hydrobasaluminite and amorphous Al(OH) 3 is suggested on the basis of SE and thermodynamic modeling analysis. These techniques also allow a quantitative estimation of the proportion of each mineral present. As a result, a complete study of the distribution of each mineral throughout the reactive material profile and the role of each phase in removing metals from the mine water can be obtained. This information is useful, not only to improve the reactive material design, but also to understand the natural processes taking place in aquatic systems affected by mining.

The elastic properties of ε-FeSi were investigated at high temperature and pressure using a combination of ultrasonic interferometry and synchrotron radiation up to 8 GPa and 1273 K. The unit-cell volumes and sound velocity data were fit to third-order finite-strain equations with adiabatic temperature conversions to maintain a thermodynamically internally consistent data set. The adiabatic zero-pressure bulk and shear moduli and their first pressure and temperature derivatives were obtained from this fitting: K S0 = 168.9(7) GPa, G 0 = 116.5(3) GPa, K S0 ′ = 6.6(2), G 0 ′ = 2.9(1), (∂K S0 /∂T) P = -0.023(1) GPa/K, (∂G 0 /∂T) P = -0.030(1) GPa/K. This study presents the first complete thermodynamically consistent set of elastic moduli and their temperature and pressure derivatives.

Demicheleite-(Cl), ideally BiSCl, is the chlorine analog of demicheleite-(Br) and is closely related to this species that occurs in the same locality. The mineral is the first natural bismuth sulfochloride discovered so far in a natural environment, and it is identical with the corresponding and already known synthetic compound. It was found in an active medium-temperature intracrater fumarole at La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. The mineral occurs as acicular to stout translucent crystals up to 0.25 mm long in an altered pyroclastic breccia, together with demicheleite- (Br), bismoclite, bismuthinite, godovikovite, panichiite, and three new minerals pending the IMA approval (IMA 2008-015, IMA 2008-039, and IMA 2008-057). The mineral is orthorhombic, space group Pnam, with a = 7.7933(10), b = 9.9293(12), and c = 3.9880(4) Å, V = 308.60(4) Å 3 (from X-ray powder data), Z = 4. The crystal habit is prismatic with {110} as the dominant form, terminated by minor faces of another prism {011}, a pinacoid {010}, and a bipyramid {111}. The color is dark red to black; the luster submetallic. It is non-fluorescent. The tenacity is brittle. The cleavage and fracture were not observed. The calculated density is 5.934 g/cm 3 . The chemical analysis obtained by WDS electron microprobe gave (wt%) Bi 72.74, Cl 11.42, Br 3.13, S 11.74, Se 0.01 wt%, total 99.04, corresponding to the empirical formula (based on 3 apfu): Bi 0.97 (Cl 0.90 Br 0.11 ) Σ1.01 S 1.02 . The crystal structure has been refined to a final R index of 0.0218 and contains Bi in sevenfold coordination inside a monocapped trigonal prism. By base sharing, these polyhedra form rows extending along [001]. The rows are connected with symmetry-related rows by sharing S-S edges of the pyramidal caps; these pairs of rows are linked to the others by sharing Cl/Br atoms. The distribution of bond lengths is close to that of the synthetic counterparts BiSCl and BiSBr, with Bi-S distances of 2.601(2) and 2.709(1) Å, and Bi-Cl/Br distances of 2.937(1) and 3.388(1) Å. The strongest 6 lines in the X-ray powder diffraction pattern [d obs (Å) (I) (hkl)] are: 2.896 (100) (121), 4.174 (45) (120), 2.684 (42) (211), 2.784 (33) (201), 1.725 (30) (411), 2.543 (27) (031). Both the mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification of the IMA (no. 2008-020).

Iron-reducing and oxidizing microorganisms gain energy through reduction or oxidation of iron, and by doing so play an important role in the geochemical cycling of iron. This study was undertaken to investigate mineral transformations associated with microbial reduction of Fe 3+ and oxidation of Fe 2+ in solid minerals. A fluid sample from the 2450 m depth of the Chinese Continental Scientific Drilling project was collected, and Fe 3+ -reducing and Fe 2+ -oxidizing microorganisms were enriched. The enrichment cultures displayed reduction of Fe 3+ in nontronite and ferric citrate, and oxidation of Fe 2+ in vivianite, siderite, and monosulfide (FeS). Additional experiments verified that the iron reduction and oxidation was biological. Oxidation of FeS resulted in the formation of goethite, lepidocrocite, and ferrihydrite as products. Although our molecular microbiological analyses detected Thermoanaerobacter ethanolicus as a predominant organism in the enrichment culture, Fe 3+ reduction and Fe 2+ oxidation may be accomplished by a consortia of organisms. Our results have important environmental and ecological implications for iron redox cycling in solid minerals in natural environments, where iron mineral transformations may be related to the mobility and solubility of inorganic and organic contaminants.

Residual elastic strain in naturally deformed, quartz-containing rocks can be measured quantitatively in a petrographic thin section with high spatial resolution using Laue microdiffraction with white synchrotron X-rays. The measurements with a resolution of 1 μm allow the quantitative determination of the deviatoric strain tensor as a function of position within the crystal investigated. The observed equivalent strain values of 800-1200 microstrains represent a lower bound of the actual preserved residual strain in the rock, since the stress component perpendicular to the cut sample surface plane is released. The measured equivalent strain translates into an equivalent stress in the order of ~50 MPa.

Samples from the surfaces of waste piles at the Vermont Asbestos Group mine in northern Vermont were studied to determine their mineralogy, particularly the presence and morphology of amphiboles. Analyses included powder X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and Raman spectroscopy. Minerals identified by XRD were serpentine-group minerals, magnetite, chlorite, quartz, olivine, pyroxene, and brucite; locally, mica and carbonates were also present. Raman spectroscopy distinguished antigorite and chrysotile, which could not be differentiated using XRD. Long-count, short-range XRD scans of the (110) amphibole peak showed trace amounts of amphibole in most samples. Examination of amphiboles in tailings by optical microscopy, SEM, and EPMA revealed non-fibrous amphiboles compositionally classified as edenite, magnesiohornblende, magnesiokatophorite, and pargasite. No fibrous amphibole was found in the tailings, although fibrous tremolite was identified in a sample of host rock. Knowledge of the mineralogy at the site may lead to better understanding of potential implications for human health and aid in designing a remediation plan.

Siberian chromite included in diamond, kimberlite, and spinel peridotite as well as Cr-spinel from garnet-spinel peridotite have been studied by single-crystal X-ray diffraction and electron microprobe analysis. Cell edges and oxygen positional parameters, u, of chromite in diamond and in kimberlite are comparable (cell edge, 8.3249-8.3390 Å; u, 0.26175-0.26213). The structural parameters of chromite in the spinel peridotite are similar to those of chromite grains from ophiolitic complexes, and those of Cr-spinel from garnet-spinel peridotite are comparable to those of Cr-spinel in lherzolitic mantle xenoliths. With the exception of the chromite in garnet-spinel peridotite, all analyzed spinels have a high Cr content. Recasting the chemical analyses according to spinel stoichiometry reveals negligible or no Fe 3+ . Chrome spinel may be present in heavy concentrates derived from serpentinized mafic and ultramafic rocks as the sole surviving primary mineral and, as such, their particular structural and chemical parameters may represent a new prospecting tool for discriminating the ultramafic source.

The crystal structure of the 2.5 hydrate MgSO 4 phase was determined by simulated annealing from laboratory X-ray powder diffraction data measured from 2-140 °2θ using CuKα radiation. The 2.5 hydrate is monoclinic, space group C2/c, with unit-cell parameters a = 18.8636(4) Å, b = 12.3391(2) Å, c = 8.9957(2) Å, β = 94.568(2)°, V = 2087.1(6) Å 3 , and Z = 16. The model was refined using fundamental-parameters Rietveld refinement, converging to R wp = 8.89%, Rp = 6.61%, R exp = 3.33%, R Bragg = 3.95%, and χ2 = 2.67. The refined structure is consistent with a formula of 2.5 H 2 O. Bond-valence calculations for the refined model show that the structure is chemically sensible. In the refined structure, [Mg(O,H 2 O) 6 ] octahedra and [SO 4 ] tetrahedra build up 2-D double-sheet slabs by sharing vertex O atoms, which are held together by inter-slab H-bonds involving (SO 4 )2- groups and H 2 O molecules coordinated with Mg 2+ cations to form the layer structure of the 2.5 hydrate phase.