gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1986.050.356.18 Crystal Structures A Re-Examination of the Structure of Ganophyllite Eggleton Richard A. Geology Department, Australian National University Canberra, A.C.T., Australia Guggenheim Stephen Department of Geological Sciences, University of Illinois at Chicago, Chicago, Illinois 60680, USA 6 1986 50 356 307 315 28 12 1984 4 10 1985 Copyright © 1986, The Mineralogical Society 1986 Abstract

The superstructure of ganophyllite has been analysed using subcell single crystal X-ray data and electron-optical observations. The full cell (supercell), space group A2/a, a = 16.6, b = 26.6, c = 50 Å, β = 94° has the approximate formula (K,Na,Ca)6+7.5(Mg,Fe,Mn)24[Si32.5Al7.5]O96(OH)1621H2O, Z = 8. A structure is proposed in which triple chains of silica tetrahedra parallel to X form narrow 2 : 1 layers with sinusoidal Mn-octahedral sheets. The triple chains are connected laterally, and across the interlayer, by pairs of inverted tetrahedra, linking to each other into four-member rings parallel to (010). Polytypes are generated by various displacements of the inverted tetrahedra.

 Keywords ganophyttite crystal structure superstructure