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Chromian mica from Sierra Nevada, Spain

Published online by Cambridge University Press:  05 July 2018

J. D. Martín-Rabios
Affiliation:
Department of Crystallography and Mineralogy, University of Granada, Spain
M. Rodriguez-Gallego
Affiliation:
Department of Crystallography and Mineralogy, University of Granada, Spain

Synopsis

Emerald green chromian 2M1 mica occurs in metamorphosed and metasomatized limestones, related to serpentinic rocks from Sierra Nevada, Spain. Chemical analysis gave: SiO2 44.51, Al2O3 27.60, TiO2 0.17, Cr2O3 3.35, Fe2O3 1.76, FeO 0.07, MnO 0.00, MgO 8.59, Li2O 0.03, Rb2O 0.01, BaO 0.01, CaO 1.71, Na2O 0.40, K2O 7.86, H2O 4.21 = 100.28. Optic properties are: pleochroism X blue, Y green, Z bluish green; refractive indices: α=1.562, β=1.611, γ=1.616 (yellow light); inclined dispersion, r > v. Orientation: second order mica. Refined parameters are a = 5.2116(6), b = 9.045(2), c = 19.97(2)Å, β = 95.7(3)°. The structure is discussed and an order in the octahedral M(1) sites is observed, but no ordering in the tetrahedral T(1) and T(2) cations is detected. The mica described is a mariposite with anoma-lously high contents of Ca and Mg.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1982

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