The regional occurrence of andalusite in metamorphic rocks of the Sierra Nevada and Inyo Mountains indicates that the maximum total pressure that the rocks have been subjected to was at or below the upper pressure limit of andalusite stability. Sillimanite is a contact metamorphic mineral and is generally restricted to metamorphic rocks associated with the older granitic rocks of the Sierra Nevada batholith, which predate the Late Cretaceous. Kyanite was found in a sample of stream sediment at one locality in the western Sierra Nevada; however, its source is unknown.

Four samples each of purified andalusites and sillimanites, including two coexistent mineral pairs, were spectrographically analyzed for trace elements, and major elements were determined for seven of the separates. Consistent partitioning patterns of certain trace elements between andalusites and sillimanites suggest that foreign-ion stabilization may play a role in survival of the polymorphs.

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