Pseudomorphous aggregates of muscovite after staurolite are characteristic of the lower sillimanite- to upper sillimanite-grade metapelites in parts of N.W. Maine. Traditional interpretations for these pseudomorphs would include retrograde metamorphism or K-metasomatism. However, mineralogic, petrographic, and field evidence clearly shows that the pseudomorphs have formed as a byproduct of a simple prograde metamorphic event.

The exact mechanism by which the pseudomorphs develop remains unclear but seems to involve the dissolution of staurolite and concommittent replacement by muscovite.

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