Rotated and Extended Model Structures in Amphiboles and Pyroxenes

A. D. Law1 and E. J. W. Whittaker
Department of Geology and Mineralogy, Parks Road, Oxford OXI 3PR
1Present address: Queen Mary College, London.

Summary: The model for the amphibole and pyroxene structures based on close-packed oxygen layers intro-duced by Thompson is investigated systematically. It is shown that different features of it can best be understood in terms of three different symbolisms: the O and S rotations of tetrahedra; the A,B, C stacking notation for close-packed layers; and the c, h notation for the relationship of close-packed layers to their neighbours. The possible stacking arrangements and their space-groups are derived systematically. Relationships between the close-packed, fully rotated, model and the extended chain model are discussed, and some important drawbacks in the former model are pointed out, especially in connection with real amphibole structures.

Mineralogical Magazine; March 1980 v. 43; no. 329; p. 565-574; DOI: 10.1180/minmag.1980.043.329.01
© 1980, The Mineralogical Society
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