Si+4 Content of natural phengites |
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Authors: | B Velde |
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Institution: | (1) Laboratoire de Pétrographie, Sorbonne, Paris |
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Abstract: | The chemical compositions of white micas separated from adjacent rocks of glaucophane and greenschist facies are compared with respect to their Si+4 content. The micas are predominantly phengitic, i.e. between muscovite, KAl2Si3AlO10(OH)2] and celadonite, K(R+2R+3)Si4O10(OH)2] in composition. Constancy of Si content in micas coming from rocks of different bulk chemical composition but closely similar physical conditions indicates that the silica content of a potassic dioctahedral mica can be used to indicate the pressure and temperature conditions of its formation. This conclusion is in part based upon previous experimental data obtained for synthetic phengites. |
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