A single-crystal study on the pressure behavior of phlogopite and petrological implications
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P. Comodi
Abstract
The structural behavior of phlogopite was studied by in situ single-crystal X-ray diffraction (XRD) in a diamond-anvil cell, using crystals of composition [(K0.91Na0.02Ba0.03) (Fe2+0.65Fe3+0.163Al0.123Mg1.81Ti0.149)Si2.708Al1.292O10OH1.725F0.175]. Lattice parameters were measured from 0.0001 to 6.5 GPa and fitted with a third-order Birch-Murnaghan equation of state (EoS). The resulting EoS parameters are: V0 = 497.1(1) Å3, K0 = 54(2) GPa-1, and K' = 7(1); a0 = 5.336(1) Å, K0 = 123(9) GPa, and K' = 3(2); b0 = 9.240(3) Å, K0 = 128(15) GPa, and K' = 3(2); c0 = 10.237(6) Å, K0 = 25(2) GPa, and K' = 5(1); the β angle increases linearly with pressure from 100.02(5) to 100.4(1)°.
The structural evolution of phlogopite was studied by comparing five structural refinements performed with intensity data collected at 0.0001, 1.2, 3.2, 5.0, and 6.0 GPa. The interlayer site, where K is located, is about 4.5 times more compressible than the T-O-T unit. At the same time, the greater compression of the octahedral layer with respect to the tetrahedral one induces an increase in tetrahedral rotation angle α from 9.29 to 11.9°.
Structural evolution with pressure yields a crystallographic rationale for the larger baric stability of K-deficient and Si-rich phlogopites, as observed from natural and experimental data.
Combined high-pressure and thermal expansion data yield the approximate EoS: V = V0 (1 + 4.6 × 10-5 ΔT - 0.0167 ΔP), where P is in GPa and T in °C. This equation was used to calculate phase equilibria in lherzolite compositions modeled in the simplified K2O-CaO-MgO-Al2O3-SiO2-H2O (KCMASH) system. The results show that the effect of phlogopite on bulk density is particularly significant at high pressure and temperature since, above the chlorite stability field, phlogopite is the only hydrous phase able to lower bulk density properties by about 0.5% with respect to the K-free bearing system.
© 2015 by Walter de Gruyter Berlin/Boston
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- Unoccupied states of pyrite probed by electron energy-loss spectroscopy (EELS)
- Tugtupite: High-temperature structures obtained from in situ synchrotron diffraction and Rietveld refinements
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- Geochemistry of oxide minerals of Nb, Ta, Sn, and Sb in the Varuträsk granitic pegmatite, Sweden: The case of an “anomalous” columbite-tantalite trend
- An X-ray and electron microprobe study of Fe, Ni, Ga, and Ge distribution and local structure in a section of the Canyon Diablo iron meteorite
- Mineralogical approaches to fundamental crystal dissolution kinetics
- Cu L3X-ray absorption spectroscopy and the electronic structure of minerals: Spectral variations in non-stoichiometric bornites, Cu5FeS4
- A new nondestructive X-ray method for the determination of the 3D mineralogy at the micrometer scale
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- The effect of TiO2on Pd, Ni, and Fe solubilities in silicate melts
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- Quantitative electron microprobe analysis of Fe3+/ΣFe: Basic concepts and experimental protocol for glasses
