Electron-Optical Studies of Phyllosilicate Intergrowths in Sedimentary and Metamorphic Rocks

S. H. White, J. M. Huggett* and H. F. Shaw
Department of Geology, Imperial College, London SW7, UK
*Present address: BP Petroleum Development Limited, Britannic House, London EC2, UK.

Abstract: The results of a microstructural study by backscattered scanning electron microscopy and a microchemical study using X-ray microprobe analysis of phyllosilicate intergrowths from sandstones, shales, metagreywackes, and low-grade schists are presented. The microstructural study revealed that the intergrowths thicken and become more coherent with metamorphic grade; the intergrowths change from incoherent to coherent in the anchizone. The increasing coherency is mirrored by an increase in the crystallinity indices of the illites/phengites. Chemical analysis of the individual intergrowth phases was difficult in the sediments and no systematic compositional variations were recorded. However, clear compositional trends with increasing metamorphic grade emerged in the phengites from the metagreywackes and schists, but in the chlorites only slight compositional changes were recorded.

Keywords: electron microscopy • electron microprobe analysis • phyllosilicates • illite • phengite • sedimentary rocks • metamorphic rocks

Mineralogical Magazine; June 1985 v. 49; no. 352; p. 413-423; DOI: 10.1180/minmag.1985.049.352.12
© 1985, The Mineralogical Society
Mineralogical Society (www.minersoc.org)