Paragenetic relations of aluminosilicates and gedrite from Fishtail Lake, Ontario, Canada

Abstract

The aluminosilicates occur in close association with gedrite in cordierite-bearing and cordierite-free schists and gneisses. In cordierite-bearing rocks, sillimanite is incompatible with gedrite; it is either completely enclosed in cordierite, or in lithologically distinct layers from those in which the gedrite occurs. In cordierite-free rocks, sillimanite and gedrite appear in close proximity, apparently because the lime content of the rock is sufficiently high so that it lies outside the cordierite composition field. Kyanite (andalusite) and gedrite are found in close association as a result of the breakdown of cordierite to kyanite (andalusite) and chlorite in a potash-deficient environment.