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Presents a study that examined the effect of pressure on hydrogen bonding in synthetic end-member clinochlore chlorite minerals using Raman spectroscopy. Methodology; Analysis of the Raman frequencies at ambient conditions; Impact of pressure on the Raman frequencies of the samples.

Presents a study which measured the Raman spectra of phase E in a diamond-anvil cell. Raman active frequencies of phase E at ambient conditions; Pressure dependence of the Raman frequencies of phase E; Discussion on the framework of Raman bands.

Raman spectra in the range 80 to 4000 cm-1 of wadsleyite II (Fo90 with 2.0 wt% H2O and Fo88 with 2.7 wt% H2O) have been measured in a diamond-anvil cell with solid rare-gas pressure-transmitting media to 51.4 GPa at room temperature. The ambient Raman spectrum of wadsleyite II is closely similar to wadsleyite modified with bands in frequency regions where the SiO4 tetrahedral and OH stretching vibrations of hydrous ringwoodite occur. The most intense, characteristic wadsleyite II modes at 709 and 911 cm-1 (Si2O7 and SiO3 symmetric stretching vibrations, respectively) shift continuously to 51.4 GPa showing no evidence for a change in the crystal structure. A striking feature in the high-pressure Raman spectra of wadsleyite II is a significant growth in intensity in the mid-frequency range (300-650 cm-1 at 10-4 GPa and 400-750 cm-1 at 51.4 GPa) under compression accompanied by the appearance of new Raman modes near 40 GPa, perhaps a result of resonance electronic Raman scattering. In the OH stretching frequency range, the Raman spectrum of wadsleyite II exhibits at least six modes and their high-pressure behavior agrees with that of Fo90 hydrous wadsleyite: OH stretching modes above 3530 cm-1 remain approximately constant up to at least 21.8 GPa whereas OH modes at frequencies <3530 cm-1 decrease with increasing pressure. The OH stretching modes are consistent with protonation of the non-silicate oxygen O2 and the O atoms surrounding the partially vacant tetrahedral site Si2, as suggested from X-ray diffraction data. [ABSTRACT FROM AUTHOR]

The occurrence and characterisation of a new member of the dundasite group are reported. Grguricite, ideally CaCr2(CO3)2(OH)4⋅4H2O, is the Cr analogue of alumohydrocalcite, CaAl2(CO3)2(OH)4⋅4H2O and occurs as lilac crusts of very fine-grained crystalline aggregates in the Pb–Ba–V mineralisation found at the Adeghoual Mine, Mibladen, Morocco (32°46′0″N, 4°37′59″W). The identification was based upon a close match with the powder X-ray diffraction data for alumohydrocalcite, the confirmation of anion components identified by Raman spectroscopy and the cation composition determined by electron-probe microanalysis. The empirical formula based upon 14 oxygen atoms per formula unit is Ca0.84Pb0.03Cr1.65Al0.39Mg0.02(CO3)2(OH)4⋅4H2O, with carbonate, hydroxyl and water contents set to those of the alumohydrocalcite stoichiometry. The fine-grained nature of the crystals (c. 0.5 μm × 0.1 μm × 5 μm) precluded a single-crystal X-ray study and both density and optical determinations. Grguricite is triclinic with space group P ${\bar 1}$. Unit-cell parameters refined from the powder diffraction data are: a = 5.724(2), b = 6.5304(9), c = 14.646(4) Å, α = 81.682(1), β = 83.712(2), γ = 86.365(2)°, V = 537.8(2) Å3 and Z = 2. The five strongest peaks in the powder pattern are [dhkl, Å (I/Imax)(hkl)]: 6.222(100)(011), 3.227(87)(020), 6.454(63)(010), 2.883(58)(005, 023, 121) and 7.208(45)(002). The mineral is named after Australian geologist Ben Grguric. [ABSTRACT FROM AUTHOR]