$USGT They are metamorphosed to amphibolite facies. Sillimanite appears in muscovite-K-feldspar-bearing metaquartzite in the sillimanite zone east of and structurally below a mapped sillimanite isograd. Sillimanite is found in pelitic schist locally outside the host-rock-defined sillimanite zone, and sillimanite occurs in granitic rocks mostly only well inside the sillimanite zone.
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