Band 93, Heft 1

Footemineite, ideally Ca 2 Mn 2+ □Mn 2 2+ Mn 2 2+ Be 4 (PO 4 ) 6 (OH) 4 ·6H 2 O, triclinic, is a new member of the roscherite group. It occurs on thin fractures crossing quartz-microcline-spodumene pegmatite at the Foote mine, Kings Mountain, Cleveland County, North Carolina, U.S.A. Associated minerals are albite, analcime, eosphorite, siderite/rhodochrosite, fairfieldite, fluorapatite, quartz, milarite, and pyrite. Footemineite forms prismatic to bladed generally rough to barrel-shaped crystals up to about 1.5 mm long and 1 mm in diameter. Its color is yellow, the streak is white, and the luster is vitreous to slightly pearly. Footemineite is transparent and non-fluorescent. Twinning is simple, by reflection, with twin boundaries across the length of the crystals. Cleavage is good on {01̅1} and {100}. Density (calc.) is 2.873 g/cm 3 . Footemineite is biaxial (-), n α = 1.620(2), n β = 1.627(2), n γ = 1.634(2) (white light). 2V obs = 80°, 2V calc = 89.6°. Orientation: X ^ b ~ 12°, Y ^ c ~ 15°, Z ^ a ~ 15°. Elongation direction is c, dispersion: r > v or r < v, weak. Pleochroism: β (brownish yellow) > α = γ (yellow). Mössbauer and IR spectra are given. The chemical composition is (EDS mode electron microprobe, Li and Be by ICP-OES, Fe 3+ :Fe 2+ by Mössbauer, H 2 O by TG data, wt%): Li 2 O 0.23, BeO 9.54, CaO 9.43, SrO 0.23, BaO 0.24, MgO 0.18, MnO 26.16, FeO 2.77, Fe 2 O 3 0.62, Al 2 O 3 0.14, P 2 O 5 36.58, SiO 2 0.42, H 2 O 13.1, total 99.64. The empirical formula is (Ca 1.89 Sr 0.03 Ba 0.02 ) Σ1.94 (Mn 2+ 0.90 □ 0.10 ) Σ1.00 (□ 0.78 Li 0.17 Mg 0.05 ) Σ1.00 (Mn 2+ 3.25 Fe 2+ 0.43 Fe 3+ 0.09 Al 0.03 ) Σ3.80 Be 4.30 (P 5.81 Si 0.08 O 24 )[(OH) 3.64 (H 2 O) 0.36 ] Σ4.00 ·6.00H 2 O. The strongest reflection peaks of the powder diffraction pattern [d, Å (I, %) (hkl)] are 9.575 (53) (010), 5.998 (100) (01̅1), 4.848 (26) (021), 3.192 (44) (210), 3.003 (14) (02̅2), 2.803 (38) (1̅03), 2.650 (29) (2̅02), 2.424 (14) (231). Single-crystal unit-cell parameters are a = 6.788(2), b = 9.972(3), c = 10.014(2) Å, α = 73.84(2), β = 85.34(2), γ = 87.44(2)°; V = 648.74 Å 3 , Z = 1. The space group is P1̅. Crystal structure was refined to R = 0.0347 with 1273 independent reflections (F > 2σ). Footemineite is dimorphous with roscherite, and isostructural with atencioite. It is identical with the mineral from Foote mine described as “triclinic roscherite.” The name is for the Foote mine, type locality for this and several other minerals.

Veins and adjacent alteration selvages in the Waits River Formation were investigated to determine whether associated mass transfer was due primarily to large-scale advection or small-scale diffusion. Samples of the vein, selvage, and adjacent wall rock were collected from the earliest and most numerous generation of veins in pelite and carbonate hosts from outcrops in the chlorite and the kyanite zones. Bulk compositions of selvages and unaltered wall rocks were compared using a reference frame defined by a combination of Zr, Ti, REEs, and U. Selvages from both outcrops typically exhibit losses of Si, K, Ba, and Rb relative to unaltered wall rock. Kyanite zone selvages show losses in Mg and Cs in addition. Differences in K, Ba, Rb, Cs, and Mg between the vein-selvage system as a whole and adjacent unaltered wall rock are possibly accounted for by development of micas in veins. The addition of Si and Ca to veins is not balanced by removal of Si and Ca from the selvages. Vein-selvage systems contain more Si than wall rock, with an overall addition of ≈40 mg Si/cm 3 to the chlorite zone and ≈55 mg Si/cm 3 to the kyanite zone. Mass balance of Si at the outcrop scale requires that >90% of the Si in quartz veins was derived externally. Quartz veins studied formed primarily by fluid flow and large-scale advective mass transfer with a relatively minor component of local mass transport by diffusion. The estimated time-integrated fluid flux necessary to produce the observed amount of quartz in veins in an entire outcrop is ≈2-6·10 6 cm 3 fluid/cm 2 rock. Mineral inclusions in garnet and fracturing of garnets adjacent to veins indicate that formation of selvages and veins initiated prior to formation of garnet and continued after the end of garnet growth.

Chemical weathering and supergene dissolution processes of Pt-bearing chromite have been studied in a lateritic weathering profile developed on ultramafic rocks in New Caledonia (southwest Pacific). The chemical distributions of alkaline earth, transition metals, and precious metals (including Pt and Pd) were determined in a weathering profile varying from bedrock at the base upward through coarse and fine saprolites, and capped by a mottled zone and a lateritic colluvial nodular horizon. Chemical analyses and mass-balance calculations suggest that progressive weathering of the parent rock is characterized by an enrichment of Fe, Co, and Mn, a segregation of Ni at the boundary between the bedrock and the coarse sapolite and in the lower part of the fine saprolite, and a depletion of Mg, Ca, Si, Al, and Cr. The higher concentration of transition metals at the interface between the coarse and fine saprolite is due to vertical transfer and precipitation at the base of the weathering profile. In such a lateritic environment, the Pt-bearing chromite grains are progressively dissolved and the Pt-group minerals (PGM) are released in the weathering mantle with a preferential depletion of Pd with regard to Pt.

The chemical weathering of ultramafic rocks has resulted in eluvial concentration of Pt-group minerals (PGM) in lateritic weathering profiles of southern New Caledonia. The Pt mineralization interpreted as being primary consists of Pt-group minerals included within chromite crystals. The occurrence of PGM as free particles in the weathering profile results from the supergene dissolution of Pt-bearing chromite (Traoré et al. 2008). Following their release in the profile, supergene dissolution processes variably affect the PGM particles. The behavior of Pt-group elements in the weathering profile is characterized by significant loss of Pd and relative enrichment of Pt indicating that Pd is more mobile than Pt in the exogenous cycle. Unstable Pt-Fe-Cu-Pd alloys and PGE oxides undergo chemical and mineralogical changes to acquire the chemical configuration of isoferroplatinum (Pt3Fe), which is the most stable Pt phase in a lateritic environment. The isoferroplatinum phase may also be dispersed throughout the weathering mantle and/or accumulated in the lower parts of profiles according to a translocation mechanism of residual Pt-rich fine particles driven by percolation of water through the connected pore spaces.

The Raman spectra of MgXO 3 -ilmenites (X = Si, Ge, Ti) were recorded up to 773 K at ambient pressure and up to 20-30 GPa at room temperature. Temperature and pressure dependence of the force constant of X-O stretching bands revealed that the expansion and compression behavior of XO 6 octahedra differed in the three ilmenites. For SiO 6 and GeO 6 octahedra, the shorter Si-O or Ge-O bonds became more lengthened with temperature and more shortened with pressure than did the longer Si-O or Ge-O bonds. In contrast, for TiO 6 octahedra, the longer Ti-O bonds became more lengthened with temperature and more shortened with pressure than did the shorter Ti-O bonds. For SiO 6 and GeO 6 at high temperatures and TiO 6 at high pressures, the cation positions moved in the direction of the c axis and tended to approach the center of the octahedra, decreasing the distortion of XO 6 . For SiO 6 and GeO 6 at high pressures and TiO 6 at high temperatures, the cations moved away from the center, increasing the distortion of XO 6 . One of the anharmonic correction terms on isochoric specific heat was also elucidated. The anharmonic effects were related to the elastic Debye temperature of the three ilmenites.

A method for conducting successful low pressure (0.3-0.5 GPa) and high temperature (900-1200 °C) experiments in the 19 mm piston-cylinder is presented. The technique is capable of running high fluid/melt experiments with minimum hydrogen loss, attaining precise, reproducible pressures (±10%), and has fast initial quench rates (>150 °C/s). These abilities are invaluable when conducting low pressure, fluid-saturated experiments such as phase equilibria, volatile solubility, and dynamic degassing experiments that are relevant to sub-volcanic magma chamber processes. A double capsule construction is also described that uses a solid oxygen buffer, and minimizes both contamination of the sample by carbon and the loss of iron in the melt to the capsule walls.

The elastic behavior and the high-pressure structural evolution of the zeolite wairakite [ideal chemical formula Ca(Al 2 Si 4 O 12 )⋅2H 2 O, space group I2/a], the Ca-analog of analcime, have been investigated by means of in-situ synchrotron X-ray powder diffraction from ambient pressure to 7.8 GPa, and upon decompression. No complete X-ray amorphization is observed up to the highest investigated pressure, and the original unit-cell parameters are recovered upon decompression. The Rietveld structural refinements of the powder patterns converged successfully up to 2.5 GPa; above this pressure, a phase transition to triclinic symmetry is observed and only the unit-cell parameters were refined. An overall reduction of about 14% of the unit-cell volume between 0.0001 and 7.0 GPa is observed, demonstrating that wairakite is much more flexible upon compression than upon heating. The pressure dependence of the cell parameters is strongly anisotropic and larger after the transition to the triclinic space group. The elastic parameters refined with a second-order Birch-Murnaghan Equation of State are V 0 = 2536(4) Å 3 , K 0 = 39(3) GPa, and V 0 = 2632(38) Å 3 , K 0 = 24(3) GPa, for the monoclinic and triclinic phases, respectively. The structure distortion of monoclinic wairakite, proceeding via tetrahedral tilting, induces deformations in the 4-, 6-, and 8-membered rings and an increase in the extra-framework Ca coordination number. A comparative discussion of the compressibility behavior of wairakite and analcime is reported.

Mineralization, involving vanadian-chromian silicates, has been studied in Lower Paleozoic, carbon-rich amphibole schists with pyrite and pyrrhotite near Pezinok, southwest Slovakia. A detailed electron microprobe study has revealed the presence of V,Cr-rich garnet, clinozoisite, and muscovite, associated with amphiboles (magnesiohornblende, tremolite, actinolite, and edenite), diopside, and albite. The garnet contains 5-19 wt% V 2 O 3 , 5-11 wt% Cr 2 O 3 , and 2-13 wt% Al 2 O 3 (16-64 mol% goldmanite, 19-36 mol% uvarovite, and 9-59 mol% grossular end-members). The garnet is unzoned or shows V-rich cores and Al-rich rims, or irregular coarse oscillatory zoning with V, Cr, and Al, locally involving Ca and Mn as well. The V,Cr-rich clinozoisite to mukhinite and “chromian clinozoisite” contains 2-9.5 wt% V 2 O 3 and 1.5-11 wt% Cr 2 O 3 ; the muscovite contains 2.5-8 wt% V 2 O 3 and 0-7 wt% Cr 2 O 3 . The mineralization originated from primarily V-, Cr-, and C-rich mafic pyroclastic rocks, affected by volcano-exhalative processes. These rocks were weakly metamorphosed during early Hercynian regional metamorphism (M1), followed by late-Hercynian contact metamorphism (M2) with crystallization of V,Cr-rich silicates, diopside, amphiboles, phlogopite, titanite, albite, quartz, carbonate, pyrite, and pyrrhotite. The youngest Alpine(?) retrograde metamorphic event (M3) is connected with production of V,Cr-poor muscovite, clinochlore, clinozoisite, pumpellyite-(Mg), prehnite, quartz, and carbonates, under prehnite-pumpellite facies conditions.

We describe an experimental apparatus used to perform deformation experiments relevant to the volcanological sciences. The apparatus supports low-load, high-temperature deformation experiments under dry and wet conditions on natural and synthetic samples. The experiments recover the transient rheology of complex (melt ± porosity ± solids) volcanic materials during uniaxial deformation. The key component to this apparatus is a steel cell designed for high-temperature deformation experiments under controlled water pressure. Experiments are run under constant displacement rates or constant loads; the range of accessible experimental conditions include: 25-1100 °C, load stresses 0 to 150 MPa, strain rates 10 -6 to 10 -2 1/s, and fluid pressures 0-150 MPa. The apparatus is calibrated against standard values of viscosity using constant-load experiments on cores of NIST (NBS) 717a borosilicate glass. We also report results of constant-displacement rate (~10 -6 m/s) experiments on porous (~70%) sintered cores of ash from the Rattlesnake Tuff. The cores of volcanic ash were deformed in experiments under ambient (“dry”) and elevated water pressures (“wet”). Dry experiments at ~870 °C show an increase in effective viscosity (10 9.5 to 10 10.4 Pa·s) with increasing strain (~30%) due to porosity reduction during compaction. Experiments under ~1-3 MPa P H₂O recover lower values of apparent viscosity (10 9.2 to 10 9.4 Pa·s) despite being run at lower temperatures (640-665 °C). The wet experiments also do not show a rise in viscosity with increased strain (decreasing porosity) as observed in dry experiments. Rather, the presence of an H 2 O fluid phase expands the window of viscous deformation and delays the onset of strain hardening that normally accompanies porosity reduction.

Menezesite, ideally Ba 2 MgZr 4 (BaNb 12 O 42 )·12H 2 O, occurs as a vug mineral in the contact zone between dolomite carbonatite and “jacupirangite” (=a pyroxenite) at the Jacupiranga mine, in Cajati county, São Paulo state, Brazil, associated with dolomite, calcite, magnetite, clinohumite, phlogopite, ancylite-(Ce), strontianite, pyrite, and tochilinite. This is also the type locality for quintinite-2H. The mineral forms rhombododecahedra up to 1 mm, isolated or in aggregates. Menezesite is transparent and displays a vitreous luster; it is reddish brown with a white streak. It is non-fluorescent. Mohs hardness is about 4. Calculated density derived from the empirical formula is 4.181 g/cm 3 . It is isotropic, n meas > 1.93(1) (white light); n calc = 2.034. Menezesite exhibits weak anomalous birefringence. The empirical formula is (Ba 1.47 K 0.53 Ca 0.31 Ce 0.17 Nd 0.10 Na 0.06 La 0.02 ) Σ2.66 (Mg 0.94 Mn 0. 23 Fe 0.23 Al 0.03 ) Σ1.43 (Zr 2.75 Ti 0.96 Th 0.29 ) Σ4.00 [(Ba 0.72 Th 0.26 U 0.02 ) Σ1.00 (Nb 9.23 Ti 2.29 Ta 0.36 Si 0.12 ) Σ12.00 O 42 ]·12H 2 O. The mineral is cubic, space group Im3̅ (204), a = 13.017(1) Å, V = 2206(1) Å 3 , Z = 2. Menezesite is isostructural with the synthetic compound Mg 7 [MgW 12 O 42 ](OH) 4 ·8H 2 O. The mineral was named in honor of Luiz Alberto Dias Menezes Filho (born 1950), mining engineer, mineral collector and merchant. Both the description and the name were approved by the CNMMN-IMA (Nomenclature Proposal 2005-023). Menezesite is the first natural heteropolyniobate. Heteropolyanions have been employed in a range of applications that include virus-binding inorganic drugs (including the AIDs virus), homogeneous and heterogeneous catalysts, electro-optic and electrochromic materials, metal and protein binding, and as building blocks for nanostructuring of materials.

The results of a new single-crystal structure refinement and of a Raman spectroscopy investigation on melanophlogite, a clathrate structure of SiO 2 , are reported. The studied sample comes from a new finding at Varano Marchesi (Parma, Italy), and occurs in small veins and pockets along fractures in a siliceous marl from a chaotic complex. Melanophlogite is invariably separated from the host rock by a thin crust of opal-CT. Raman spectroscopy was done to investigate the guest molecules that are hosted in the cages of the structure. In the Varano Marchesi melanophlogite, only CH 4 is present in the clathrate structure. During a comparative investigation of melanophlogite from different geological setting (Racalmuto, Sicily, Italy), H 2 S also was found, together with CH 4 , in the cavities of the structure. A single-crystal X-ray refinement of the Varano Marchesi sample was done using the Pm3̅n symmetry of β-melanophlogite [a = 13.399(2), R 4σ = 4.7%]. According to the site refinement from X-ray diffraction results, CH 4 occupies 71 and 91% of the 5 12 and 5 12 6 2 site cavities, respectively. The Varano Marchesi melanophlogite formed as a result of low-temperature hydrothermal activity. The mineral growth occurred at the expense of opal, in connection with CH 4 flux through the porous material.

The crystal structure of direnzoite, a new natural zeolite found in the cavities of a xenolitic rock from the Massif Central (France) is reported. Apparently, direnzoite was formed throughout a process of hydrothermal crystallization within the vugs of a highly porphyric basalt. The determination of the crystal structure of this new zeolite was at the limits of the existing experimental techniques because of the paucity of available specimen, mainly composed of three tiny aggregates of fibrous microcrystals. The structure of direnzoite, solved by powder methods, was shown to be the K-dominant equivalent of the synthetic zeolite ECR-1 with a framework composed of layers of mordenite (MOR) and mazzite (MAZ) connected in a regular 1:1 stacking sequence with assigned framework topology EON. The chemical composition of direnzoite determined from the structure refinement is (Na 0.94 K 6.62 Mg 1.42 Ca 2.24 )(Si,Al) 60 O 120 ·36.8H 2 O. The unit cell determined from the Rietveld structure refinement is a = 7.57887(18) Å, b = 18.20098(57) Å, c = 26.15387(83) Å, and the space group is Pmmn. Six extra-framework sites and 14 water molecules were identified within the zeolite micropores. Three extra-framework sites are occupied by K + ions. The others are occupied by Na + , Ca ++ , and Mg ++ . Although direnzoite and ECR-1 share the same framework, the distribution of their extra-framework cations is rather different. In direnzoite, there are no equivalent positions to C1, C2, and C4 positions found in ECR-1. Only sites C3 and C3b correspond respectively to K3 and Ca in direnzoite. In direnzoite, K1, K2, and Na correspond to water molecules sites (H 2 O1, H 2 O11, and H 2 O8, respectively) in ECR-1.

Apparent superlattice reflections obtained in electron diffraction patterns of modulated calcite and dolomite have been ascribed to local domains of various different metastable Ca-Mg ordering schemes that are not known as macroscopic phases. We show that the type “c” reflections in diffraction patterns of supposed superstructures can in fact be produced by superposition of diffraction from the host crystal and that from domains that are in an orientation related to the host by twinning on (104). From details of the additional reflections present, we deduce that the carbonate anions are orientationally disordered in the twin nanodomains, which have the R3̅m space group of high-temperature disordered calcite. This twinning can explain the diffraction ascribed to type “γ”/”μ”/”ν” superstructures, and resolves controversies over the occurrence of these purportedly different superstructures. The relationships between composition, orientational order of the carbonates, molar volume and known macroscopic structures, and the possibility of interfacial strain reduction by static disorder in the twin domain, are discussed. We stress the importance of checking for presence of twinned nanodomains using microdiffraction before attributing an apparent superstructure modulation to local cation ordering. High-resolution imaging may not be diagnostic, since overlap of small domains and host matrix can give Moiré patterns that resemble superlattice fringes.

The density functional theory (DFT) based orthogonalized linear combination of atomic orbitals (OLCAO) method is used to study the electronic structure and spectroscopic properties of three alumino silicate polymorphs (Al 2 SiO 5 ), andalusite, sillimanite, and kyanite. These polymorphs are precursors to mullite, which is an excellent refractory material. The electronic structure results include the band structure, total and partial density of states, bond order, and Mullikan effective charge (Q*), whereas the spectroscopic properties include X-ray absorption near-edge-structure (XANES), and the complex optical dielectric functions (ε 1 + iε 2 ) for each polymorph. For the XANES calculations, we use a supercell approach and account for the electron-core hole interaction. Our calculations show that the polymorphs are insulators with direct band gaps of 5.05, 5.21, and 5.80 eV for andalusite, sillimanite, and kyanite, respectively. The calculated refractive indices (n) for each material are in agreement with experimental values from the literature. Results on the XANES spectral calculations (K-edge and L-edge) for all crystallographically nonequivalent ions in the polymorphs are presented. It is shown that to achieve excellent agreement with the experimentally measured spectrum, a weighted sum of the spectra from crystallographically inequivalent sites must be used. The analysis of the XANES spectra based on differences in the local bonding environments are provided.

Crystal-size and spatial distributions of minerals in metamorphic rocks provide insight into their nucleation, growth environment, and the metamorphic evolution of their host rocks. Episodic nucleation and growth histories for garnets in eclogites from the Dabie orogen are revealed by variations in crystal size, geochemical zoning, and mineralogy of inclusions in garnets. The studied garnets show pseudo-lognormal crystal-size distributions (CSDs), prograde chemical zoning patterns indexed by mineral inclusions, and are mainly distributed at random. Constant growth rate for each episode is proposed based on the mineralogy of inclusions in garnets and the chemical zoning patterns. The CSD shapes were evaluated in terms of a size-dependent proportionate growth model and a thermally accelerated, diffusion-controlled model but neither is consistent with the geochemical data and the concordant occurrence of mineral inclusions in garnet. Initial increasing nucleation rate followed by a subsequent, medial stage of nearly constant growth and finally declining nucleation rate is inferred from the CSD data. This study suggests that linking chemical analysis with textural analysis is crucial to avoid misleading interpretation solely through CSD shapes of minerals in metamorphic rocks.

The thermodynamic mixing properties of the pyrope-grossular solid solution show large deviations from ideality, which could be partly related to Ca-Mg order/disorder. In this study, synthetic pyrope-grossular garnets with X Mg = 1.00, 0.91, 0.75, 0.50, 0.24, 0.10, and 0.00 are observed using 17 O 3QMAS, 27 Al MAS, and 29 Si MAS NMR to examine Ca-Mg order/disorder behavior and crystal chemical variations. The 17 O 3QMAS NMR spectra show four distinct resonances, assigned to four different local oxygen coordination environments; two resemble end-member garnets (oxygen bonded to two Mg or two Ca) and two are intermediate (oxygen bonded to one Ca and one Mg), indicating that there are two distinct bond distances for the Mg-O and/or Ca-O bonds through the entire solid solution. Noticeable changes in the NMR peak position for two of the oxygen sites suggest that as X Mg increases, the longer Ca-O bond shortens. The relative areas for the different oxygen sites are close to those predicted using a model of random Ca/Mg mixing. The maximum allowed reduction in configurational entropy from first neighbor Ca-Mg ordering is insignificant relative to other configurational entropy reductions and excess vibrational entropy. These conclusions are not inconsistent with published theoretical calculations suggesting some Ca-Mg ordering that involves correlations beyond the first neighbor, as suggested by published theoretical calculations. Even at 18.8 Tesla, the 27 Al MAS NMR spectra do not resolve different local Al sites with varying combinations of X cation neighbors. The 29 Si MAS NMR spectra have resonance broadening, probably caused by the addition of 0.15 wt% Fe 2 O 3 in the synthetic samples, and are consistent with published results suggesting a small degree of Ca-Mg ordering that is not reflected in the 17 O NMR spectra.

Natural mid-ocean ridge basalt (MORB) samples recovered from diamond-anvil cell (DAC) experiments performed between 33 to 89 GPa and 1700 to 2600 K were studied with a transmission electron microscope (TEM). We used the focused ion beam (FIB) lift-out technique to prepare the recovered high-pressure, laser-heated samples for TEM study. Observations of TEM sections show the presence of five phases for samples transformed at pressures ranging from 33 to 45 GPa: Al-bearing Mg-perovskite, Ca-silicate perovskite, stishovite, and two Al-rich phases. The Al-rich phases were identified by selected area electron diffraction (SAED) patterns and chemical composition analysis, and include the new aluminous (NAL) phase with hexagonal structure and the calcium ferrite (CF) type phase. Chemical analyses obtained by analytical transmission electron microscopy (ATEM) show that Mg-silicate perovskite is the major host for Al, with significant amounts also distributed between the CF-type and NAL phases, and less than 1 wt% in stishovite. Beyond pressures of ~40 GPa (~1100 km depth), the Al content of Mg-perovskite and CF-type phase increases. Between 45 and 50 GPa, the NAL phase disappears. This mineralogical change may explain reported seismic anomalies in subduction zones at mid-mantle depths.

Barioperovskite, ideally BaTiO 3 , is a new member of the perovskite group. It is found as micro- to nano-crystals in a host of amorphous material contained within hollow, tubular inclusions in benitoite from the Benitoite Mine, San Benito County, California, U.S.A. The mean chemical composition determined by electron-microprobe analysis is (wt%) BaO 65.46, TiO 2 34.57, SiO 2 0.89, sum 100.92. The empirical formula calculated on the basis of 3 O is Ba 0.97 Ti 0.98 Si 0.03 O 3 . Barioperovskite is orthorhombic, Amm2; a = 3.9874 Å, b = 5.6751 Å, c = 5.6901 Å, V = 128.76 Å 3 , and Z = 2. The electron backscattered diffraction pattern is an excellent match to that of synthetic BaTiO 3 with the Amm2 structure. The strongest calculated X-ray powder diffraction lines from the synthetic BaTiO 3 data are [d in Å, (I), hkl] 4.018 (18) (011), 2.845 (30) (002), 2.830 (100) (111), 2.316(20) (102), 2.312 (23) (120), 2.009 (28) (022), 1.640 (17) (113), 1.637 (19) (131), 1.633 (18) (202), and 1.415 (15) (222). The mineral is named after its composition, a Ba-dominant member of the perovskite group.

The unusual luminescence of particular varieties of natural pink calcite (CaCO 3 ) samples was studied by laser-induced time-resolved luminescence spectroscopy at different temperatures. The luminescence is characterized by intense blue emission under shortwave UV lamp excitation with an extremely long decay time, accompanied by pink-orange luminescence under longwave UV excitation. Our investigation included optical absorption, natural thermostimulated luminescence (NTL) and Laser-Induced Breakdown Spectroscopy (LIBS) studies. Two luminescence centers were detected: (1) a narrow violet band, with λ max = 412 nm, Δ = 45 nm, two decay components of τ 1 = 5 ns and τ 2 = 7.2 ms, accompanied by very long afterglow, and an orange emission band with λ max = 595 nm, Δ = 90 nm, and τ = 5 ns. Both luminescence centers are thermally unstable with the blue emission disappearing after heating at 500 °C, and the orange emission disappearing after heating at different temperatures starting from 230 °C, although sometimes it is stable up to 500 °C in different samples. Both centers have spectral-kinetic properties very unusual for mineral luminescence, which in combination with extremely low impurity concentrations prevent their identification with specific impurity related emission. The most likely explanation of these observations may be the presence of radiation-induced luminescence centers. The long violet afterglow is evidently connected with trapped charge carrier liberation, with their subsequent migration through the valence band and ultimate recombination with a radiation-induced center responsible for the unusual violet luminescence.

Fourier transform infrared (FTIR) microspectroscopy of igneous and metamorphic fluorapatites shows measurable carbonate in all specimens. All specimens show the presence of the type A1 and A2 (carbonate for columnar anion, Fleet et al. 2004) and the type B (carbonate for phosphate) substitutions in the carbonate ν 3 domain (1400-1600 cm -1 ). This is the first report of the type A2 substitution in naturally occurring apatites. Spectra also show ν 3 carbonate peaks that have not been unambiguously assigned. In some spectra, two doublets can be resolved, indicating two different B-type substitutions. The presence of multiple B-type substitutions in infrared spectra is in accord with the recognition of different mechanisms of substitution of the carbonate for the phosphate tetrahedron and explains the scatter observed in published data. Consideration of crystal structural details shows site symmetry of the carbonate group to be C s rather than C 2v as has been previously assumed. Decent of C s symmetry from D3h through C 2v lifts degeneracy and preserves orthogonality of ν 3 doublets. Extra type B peaks are not due to lower site symmetry, and Davydov splitting can be ruled out. Results demonstrate that carbonate contents of apatites from pegmatites and cumulate mafic magmas are well within analytical capability, opening another line of inquiry into CO 2 behavior in igneous and metamorphic rocks. The type A1 substitution shows the most promise for thermodynamic calculations that would allow extraction of CO 2 activities. Analyses show similar ratios of water to carbon dioxide activities recorded in pegmatite apatites.

The crystal structure of diopside has been determined at various pressures to 10.16 GPa. The results to 5 GPa are consistent with Levien and Prewitt (1981). The crystal structures have been analyzed using the geometric pyroxene model of Thompson and Downs (2004), the anion packing algorithm of Thompson and Downs (2001), and a new algorithm that quantifies the distortion of observed pyroxenes from their geometric model equivalents. Diopside is shown to compress via three main mechanisms: isotropic scaling, kinking of the tetrahedral chains, and collapse of the M1 chain toward its axis. The kinking of the chains accounts for most of the anisotropy of compression observed in the a-c plane, and the collapse of the M1 chain explains the anisotropy seen in the b-c plane. Model behavior is shown to reproduce many of the observations of previous workers. Anion-anion interactions are shown to be important in the distortion of observed diopside from its geometric model equivalent.

Quantitative microstructural analysis of zircon using electron backscatter diffraction (EBSD) requires a comparison of empirically collected electron backscatter patterns with theoretical patterns or “match units” derived from known crystallographic parameters. There are 23 possible crystallographic data sets for zircon, and associated match units, derived from natural and synthetic zircon and from theoretical calculations over a range of pressures and different rare earth element (REE) compositions. A systematic assessment of these match units has been undertaken by EBSD analysis of each of four zircons from a range of geological environments combined with principal components analysis and self-organizing map networks. Comparison of the different match units shows a systematic relationship across all samples that are related to changes in unit-cell dimensions associated with pressure and compositional variations. Systematic variations in the data generated from 96 EBSD maps, each comprising 10 000 electron backscatter patterns, indicate that match units associated with increasing pressure or REE dopants yield poorer quality EBSD data. The match units from low-pressure, undoped, natural zircon consistently yield the best EBSD results and are recommended for natural zircon EBSD studies irrespective of the zircon source or U content. The results provide a clear strategy for optimizing the acquisition and analysis of EBSD data from zircon from both crustal and mantle sources. In addition, the developed approach to match unit analysis may be applied to all other crystalline materials, potentially optimizing EBSD analyses from a range of materials.

The crystal structure of a natural jadeite, NaAlSi 2 O 6 , was studied at room temperature over the pressure range 0-9.17 GPa using single-crystal X-ray diffraction. Unit-cell data were determined at 16 pressures, and intensity data were collected at nine of these pressures. A third-order Birch-Murnaghan equation of state fit to the P-V data yielded V 0 = 402.03(2) Å 3 , K 0 = 136.5(14) GPa, and K 0 ' = 3.4(4). Jadeite exhibits strongly anisotropic compression with unit strain axial ratios of 1.00:1.63:2.10. Silicate chains become more O-rotated with pressure, reducing ∠O3-O3-O3 from 174.7(1)° at ambient pressure to 169.2(6)° at 9.17 GPa and bringing the anions of jadeite closer to a cubic closest-packed arrangement. No evidence of a phase transition was observed over the studied pressure range. In an effort to understand pyroxene compressibilities, selected clinopyroxene bulk moduli were plotted against ambient unit-cell volumes. Two trends were identified and are explained in terms of differences in M2-O3 bonding topologies and the geometric relationship of the bonds with tetrahedral rotation in the silicate chains. Bonds positioned to favor the tetrahedral rotation upon compression are termed “sympathetic,” whereas bonds positioned to resist the rotation are termed “antipathetic.” Examination of the different pyroxene structures indicates that structures containing antipathetic M2- O3 bonds are less compressible than those with only sympathetic M2-O3 bonds. This behavior has not been previously recognized.

Low-OH apatite of the compositional range Ca 4.99-5.06 (PO 4 ) 2.98-3.00 F 0.51-0.48 Cl 0.38-0.36 OH 0.14-0.12 was synthesized and characterized structurally by synchrotron-based single-crystal X-ray diffraction (XRD), and multiple nuclear magnetic resonance (NMR) spectroscopic techniques. The average structure is hexagonal with space group P6 3 /m. The presence of scattering in the single-crystal diffraction data set, which is incommensurate within the average hexagonal structure, suggests the presence of localized short-range monoclinic domains. Complex lineshapes in the 31 P and 19 F MAS NMR spectra are also consistent with the presence of an incommensurate phase. No evidence was detected for splitting of the Ca2 site into two distinct sites (as had been previously reported for hexagonal ternary apatites). Structure refinement and 19 F{ 35 Cl} TRAPDOR NMR experiments verified intercolumnal neighboring of F and Cl atoms (inter-column distance of 2.62 Å) within this low-OH- apatite suggesting that long-range neighboring of F and Cl within the apatite anion channels is feasible.

The crystal structure of deuterated topaz [topaz-OD; Al 2 SiO 4 (OD) 2 ], synthesized at 10 GPa and 800 °C, has been determined using neutron powder diffraction at pressures up to 7.5 GPa. The linear axial compressibilities obtained from regressions of the lattice constants vs. pressure are β a = 1.87(1) × 10 -3 GPa -1 , β b = 1.71(1) × 10 -3 GPa -1 , and β c = 2.73(1) × 10 -3 GPa -1 . The occupancy of the D1 site was found to be greater than that of D2, as shown independently using neutron diffraction and infrared spectra at ambient conditions. A bifurcated hydrogen bond involving the D1 site, O4-D1···O2 and O4- D1···O3, and a trifurcated hydrogen bond involving D2 site, O4-D2···O1, O4-D2···O2, and O4-D2···O4 are proposed for hydrogen-bond donor and acceptor pairs in addition to those reported previously. The observed pressure dependences of the hydrogen-bonding geometry show that these donor and acceptor pairs are classifiable into two types of interaction: (1) those that strengthen as a function of pressure (O4-D1···O3, O4-D2···O2, and O4-D2···O4) and (2) those that weaken (O4-D1···O1 and O4-D2···O1). These results also demonstrate that the reason for the contrasting behavior of the ν(OH) between F-rich natural topaz and topaz-OH are both the cooperative effect, O4-D2···O4-D1···O3, and the increasing Al-O4 distance.

Structural data on silicate, aluminate, and aluminosilicate melts are difficult to measure and understand at high temperature. X-ray absorption spectroscopy (XAS) performed in situ at high temperature has been used to probe the local environment of low-Z elements (Al, Si, and Ca). For fully tetrahedral network glasses, CaAl 2 Si 2 O 8 (anorthite) and CaAl 2 O 4 , the modifications in the Al K-edge spectra with increasing temperature can be attributed to a structural rearrangement of the network or to an increase of fivefold-coordinated Al. For the Ca 3 Al 2 O 6 composition, where Al is localized in a depolymerized tetrahedral site associated with non-bridging O atoms, XAS spectra at the Al K-edge are barely affected by temperature. Depending on the composition, Ca K-edge spectra investigated in these experiments allow us to follow changes in the distortion of the Ca sites in melts at high temperature. The structural modifications at both short and intermediate range upon melting are well shown by these XAS measurements.

The origin of sulfite (S 4+ ) species in silicate glasses was evaluated using XANES at the S K-edge. Systematic investigations show that the presence of S 4+ species in silicate glasses is an analytical artifact related to changes in the sulfur species caused by irradiation with an electron beam during EMPA or by irradiation with an intense focused X-ray beam during synchrotron analysis. The data shown here indicate that S 2- and S 6+ are the only significant sulfur species occurring in silicate glasses synthesized under geologically relevant conditions.

The hollandite structure-type has received considerable attention as a nuclear waste form for the incorporation of radioactive 135 Cs and 137 Cs, both of which are important fission product radionuclides in the high-level nuclear waste generated by the reprocessing of used nuclear fuel. A critical concern has been the effects of high doses of ionizing radiation from incorporated Cs on the long-term structural stability of the hollandite structure. Optimization of the synthesis conditions has resulted in the hollandite stoichiometry of Ba 0.85 Cs 0.26 Al 1.35 Fe 0.77 Ti 5.90 O 16 . To evaluate the effect of Cs-beta-decay on this stoichiometry, we have simulated the ionizing radiation using 200 kV electron beam using transmission electron microscopy (TEM) at 298 and 573 K. Complete amorphization was achieved at doses of 1.1 × 10 14 and 1.8 × 10 14 Gy at temperatures of 298 and 573 K, respectively. Electron energyloss spectroscopy (EELS) of the Cs M-edge revealed the selective loss of Cs at the maximum doses. Hollandite irradiated using gamma rays, ~10 6 Gy, which has defects associated with the formation of Ti 3+ and O 2̅ had a dissolution rate similar to that of the pristine hollandite, suggesting that the initial stage of defect formation does not influence chemical durability. Because the accumulated dose in the hollandite with 5 wt% of radioactive 137 Cs 2 O is estimated to be ~2.0 × 10 10 Gy after 500 years, the hollandite structure should be stable under the conditions anticipated for geologic disposal.

After a review of history, it is shown that in a comprehensive 1-atm study by McBirney and Naslund (1990), the Skaergaard liquidus temperature is linear from LZa to UZa on stratigraphic height when corrected to pressure. The augite saturation point at LZa/b has the same liquid composition in terms of plagioclase An content as the corresponding point in the Kiglapait intrusion, studied at 5 kbar by Morse et al. (2004). This temperature, 1203 °C at 5 kbar, is transformed to the Skaergaard pressure at LZa/b to a value of 1173 °C. From this fixed point, all other liquidus temperatures at Skaergaard are scaled to mean plagioclase core compositions from a detailed study by Toplis et al. (2007). All such points from LZb to UZa lie, within experimental error, on the regression from McBirney and Naslund, and the further points in UZb and UZc also agree. Plagioclase-based temperatures at the base of LZa exceed the earlier estimates by ~24 °C and imply a possible temperature of 1210 °C in the Hidden Zone. These results provide a good interim model for the Skaergaard liquidus pending further experimental study at the liquidus.