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The transition zone is dominated by polymorphs of olivine, wadsleyite, and ringwoodite, which are to date considered the main water carriers in the Earth's mantle. Despite considerable studies on water solubility and its impact on physical properties of the two minerals, knowledge of their hydrogen defects and framework behavior at high temperature and high pressure is still lacking. Here, we systematically assess this issue, by in situ high-temperature (20–800 °C) infrared spectroscopic studies, in situ high-temperature (20–800 °C) and high temperature-pressure (14.27 and 18.84 GPa, 20–400 °C) Raman spectroscopic studies on the iron-bearing wadsleyite and ringwoodite. The results show that dehydrogenation in wadsleyite happens at a higher temperature than in ringwoodite. The infrared absorption patterns of hydrogen defects in wadsleyite and ringwoodite are temperature sensitive, resulting from hydrogen defects transfer and site-specific stabilities. As for the framework, it is more sensitive to temperature and pressure for ringwoodite than wadsleyite. These results provide new knowledge about hydrogen defects and framework of wadsleyite and ringwoodite at high temperature and high pressure, which is indispensable for understanding water solubility and its impacts on physical properties of these two minerals. [ABSTRACT FROM AUTHOR]

Zinconigerite-2N1S ZnSn2Al12O22(OH)2 and zinconigerite-6N6S Zn3Sn2Al16O30(OH)2 are two new minerals with different numbers and ratios of nolanite (N) and spinel (S) modules. Both phases have been discovered in the Xianghualing skarn, Hunan Province, China. Zinconigerite-2N1S (zn-2N1S) and zinconigerite-6N6S (zn-6N6S) are named for their chemical composition, number, and ratios of N-S modules, according to the nomenclature of the nolanite-spinel polysomatic series of Armbruster (2002). Both phases occur as aggregates, sub-to-euhedral crystals, with maximal dimensions up to 100 μm, within fluorite aggregates, and they are closely associated with phlogopite, chrysoberyl, magnetite, cassiterite, margarite, and nigerite-taaffeite group minerals. They do not show fluorescence in long- or short-wave ultraviolet light. The calculated densities are 4.456 g/cm3 for zn-2N1S and 4.438 g/cm3 for zn-6N6S. Optically, zn-2N1S is uniaxial (+) with ω = 1.83(1), ε = 1.84(2); zn-6N6S is uniaxial (+) with ω = 1.85(1), ε = 1.87(2) (λ = 589 nm). Their chemical compositions by electron-microprobe analyses give the empirical formulas (Zn0.734Mn0.204Na0.122Ca0.063Mg0.044)Σ1.166(Sn1.941Zn0.053Ti0.007)Σ2 A l 11.018 F e 0.690 3 + Z n 0.200 S i 0.092 12 O 22 (O H) 2 for zn-2N1S and Z n 1.689 M n 0.576 M g 0.328 F e 0.407 3 + Σ 3 S n 1.882 Z n 0.047 T i 0.071 Σ 22 A l 14.675 F e 1.088 3 + N a 0.13 C a 0.086 S i 0.017 Σ 15.996 O 30 (O H) 2 for zn-6N6S. Both phases have trigonal symmetry; the unit-cell parameters of zn-2N1S (P3m1) and zn-6N6S (R3m), refined from single-crystal X‑ray diffraction data, are, a = 5.7191(2) and 5.7241(2) Å, c = 13.8380(6) and 55.5393(16) Å, V = 391.98(3) and 1575.96(12) Å3, and Z = 1 and 3, respectively. The structure of zn-2N1S is characterized by the alternating O-T1-O-T2-O-T1 layers stacked along the c-axis, showing the connectivity of N-S-N. The polyhedral stacking sequence of zn-6N6S is 3 × (O-T1-O-T2-O-T2-O-T1), reflecting a N-S-S-N-N-S-S-N-N-S-S-N connectivity of the polysomatic structure. By contrast, the structure of zn-2N1S shows the elemental replacements of Al → Sn and Al → Zn, suggesting the substitution mechanism of 2Al → Zn + Sn. The complex substitution of Zn by multiple elements (Al, Fe3+, Mn, Mg) in the structure of zn-6N6S, is coupled with the low occupancy of Al5-octahedra. Fe3+ → Al substitution occurs in Al1-tetrahedra of both zn-2N1S and zn-6N6S. The new polysomes, zn-2N1S and zn-6N6S, likely crystallized under F-rich conditions during the late stages of the Xianghualing skarn formation. The discovery of zn-2N1S and zn-6N6S provides new insights into the crystal chemistry of the N-S polysomatic series and its origin. [ABSTRACT FROM AUTHOR]

Knowledge of volatile cycling is vital to understanding the evolution of the planet and the life it supports. Although it has been gradually accepted that the mantle is a vast storehouse of H2O and other volatiles, the impact of coexisting volatiles on the thermal stabilities of OH and the lattice of the host mineral is still poorly understood. Phlogopite is one of the few hydrous minerals capable of carrying both water and halogens into the mantle. Previous observations from both experiments and textural relationships in natural samples have indicated that F-rich phlogopite can be stable under ultrahigh-temperature conditions. Here, the impact of F on the thermal stability of phlogopite was investigated via XRD, Raman, and IR spectroscopy from room temperature to 1000 to 1200 °C. Based on the experimental results from F-poor and F-rich natural phlogopites, we show that about 4 wt% F can increase the breakdown temperature of phlogopite by 100 °C under ambient pressure. The impact mechanism mainly involves preventing OH and lattice softening at high temperatures. This study reveals the links between F and the behavior of OH and phlogopite lattice, which is important for constraining volatile cycling, as well as the role of F in the physical and chemical properties of the upper mantle. [ABSTRACT FROM AUTHOR]

Chukochenite, (Li0.5Al0.5)Al2O4, is a new mineral species from the Xianghualing skarn, Hunan Province, southern China. It occurs as subhedral to euhedral crystals up to 200 μm across in the green rock of Xianghualing skarn, closely associated with fluorite, phlogopite, chrysoberyl, margarite, chlorite, ferronigerite-2N1S, and zinconigerite-2N1S. The crystals are colorless and transparent with a vitreous luster. Chukochenite is brittle with irregular fracture, has a Mohs hardness of 8, and shows light red fluorescence under 253.7 nm UV radiation and light green fluorescence under 365 nm UV radiation. The calculated density is 3.771 g/cm3. Chukochenite is optically biaxial (–) with α = 1.79(2), β = 1.82(2), and γ = 1.83(2) (589 nm). The calculated 2V is 60°, with the optical orientations X, Y, and Z parallel to the crystallographic a, b, and c, respectively. Electron microprobe analysis (Li by LA-ICP-MS) yielded in wt% Al2O3 80.70, Fe2O3 8.16, Li2O 3.68, ZnO 3.25, MnO 2.49, MgO 1.70, Na2O 0.11, CaO 0.08, TiO2 0.02, K2O 0.01, and Cr2O3 0.01 (total 100.24 wt%), giving an empirical formula [(Li0.355Al0.138Na0.005Ca0.002)Σ0.5(Al0.145Fe+0.1473 Mg0.061Zn0.058Mn0.051Si0.001)Σ0.463]Al2O4 on a basis of 4 O atoms per formula unit. Chukochenite is orthorhombic, Imma, a = 5.659 (1), b = 16.898 (1), c = 7.994 (1) Å, V = 764.46 (8) Å3, and Z = 12. The nine strongest lines of powder XRD [d in Å (I) (hkl)] are: 2.405 (53) (231); 1.996 (29) (260); 1.535 (77) (303); 1.413 (100) (264); 1.260 (52) (2 12 0); 1.068 (36) (1 13 4); 1.039 (61) (503); 0.999 (59) (008); and 0.942 (35) (3 13 4). Chukochenite has a framework structure of spinel with low symmetry (orthorhombic Imma) due to the ordering of Li cations over octahedrally coordinated sites, which has not been previously reported for synthetic (Li0.5Al0.5) Al2O4. This structure type is based on a framework of AlO4 tetrahedra, AlO6, and LiO6 octahedra. AlO6 edge-sharing octahedra form chains along the a axis. AlO6 octahedra and LiO6 octahedra in a 2:1 ratio share edges, forming octahedral chains along b. These octahedral chains are connected by AlO4 tetrahedra and each corner of an AlO4 tetrahedron shares with three AlO6 octahedra or two AlO6 + one LiO6 octahedra. The discovery of chukochenite adds a new perspective on the cation ordering and the mechanism of luminescence and magnetism in (Li0.5Al0.5)Al2O4. [ABSTRACT FROM AUTHOR]

The behavior of structural OH in clinopyroxene (augite and omphacite) during successive heating has been investigated by in situ micro-FTIR measurements under temperatures ranging from room temperature to 500[degrees]C at 100[degrees]C increment. The first group of OH band (3620-3640 [cm.sup.-1]) exhibits a systematic decrease of peak position upon successive heating, while the other two groups (3520-3535 and 3450-3465 [cm.sup.-1]) show only little change. Both augite and omphacite display a decrease of integral absorbance of OH fundamental stretching vibration upon successive heating. The IR spectra of OH band are reversible when the temperature decreases from 500[degrees]C to room temperature, suggesting that changes in IR indicate changes in molecular state of OH. Based on: (1) the decreases of integral absorbance of OH bands with increasing temperature, and (2) comparison with Paterson's relationship (Paterson 1982), we suggest that OH absorption coefficients are temperature dependent, so it is necessary to apply different absorption coefficients when determining OH content from Beer-Lambert law at different temperatures and sample temperatures should be reported in quantitative IR studies Keywords: IR, varying temperature, OH, clinopyroxene DOI: 10.2138/am.2010.3501