A Re-Examination of the Structure of Ganophyllite

Richard A. Eggleton and Stephen Guggenheim
Geology Department, Australian National University Canberra, A.C.T., Australia
Department of Geological Sciences, University of Illinois at Chicago, Chicago, Illinois 60680, USA

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

Mineralogical Magazine; June 1986 v. 50; no. 356; p. 307-315; DOI: 10.1180/minmag.1986.050.356.18
© 1986, The Mineralogical Society
Mineralogical Society (www.minersoc.org)