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spotting


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Dark-coloured, rounded areas, up to 2 mm in diameter and sometimes larger, found on the surface of slaty cleavage in low- to medium-grade contact metamorphic rocks (see contact metamorphism) of pelitic composition. Many spots are graphite-rich, having formed by metamorphic aggregation from organic material originally disseminated through the starting sedimentary shale. Rocks may also have a spotty appearance when andalusite is beginning to appear in contact-metamorphosed pelites.

Subjects: Earth Sciences and Geography.


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