Abstract

Kyanite and chloritoid occur together in two units of metaconglomerate in the Appalachian Piedmont of Maryland. Surrounding pelitic schists consist chiefly of chlorite, albite, epidote, muscovite, and quartz with chloritoid and garnet present locally; kyanite is lacking. Black graphitic slate closely associated with kyanite- and chloritoid-bearing metaconglomerate contains abundant chloritoid but no kyanite, even though it is an Al-rich rock. Differences in MgO and alkali content are sufficient to explain the presence of kyanite in the metaconglomerates and its absence from associated pelitic schists. The reducing environment in the graphitic slates may explain why kyanite is not found there but forms in the more oxidized metaconglomerates.

The postulated metamorphic reaction forumla in metaconglomerate appears to coincide with a reaction of the type forumla in surrounding pelitic schists.

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