Amesite

Amesite is a magnesium-aluminum silicate hydrate and a member of the kaolinite-serpentinite mineral group. This layer silicate occurs as white, colorless, pale green to pale blue, also pink to lilac (chromian), foliated aggregates of platy, triclinic crystals exhibiting a greasy luster.

Amesite is formed as a product of low-grade metamorphism of aluminum- magnesium-rich rocks and is often associated with hornblende, actinolite, biotite, almandine, corundum, magnetite, cordierite, and chlorite. Amesite was first described from the type locality Chester Emery Mines, Chester, Hampden Co., Massachusetts, USA, and was named for one of the original mine owners, James T. Ames (1810-1883). The emery deposits in Hampden County are located on a major thrust fault along which ultramafic rocks have been juxtaposed against more aluminous rocks. Hydrothermal fluids moving along the thrust caused low-grade metamorphism and alteration resulting in formation of the deposits. Other notable localities include: Tracy mine, Negaunee, Marquette County, MI, USA; Tiger, AZ, USA; Missoula, Missoula County, Montana, USA; chromian amesite occurs at the Saranovskaya Deposit, Middle Ural Mountains, Russia.

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