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common silicate mineral that occurs in crystalline limestones near their contacts with igneous rocks, and in beds of marble and calcsilicate granulite that are associated with gneiss and mica schist. Fine glassy crystals coloured yellow, green, or brown have been found in the Ala Valley in the Piedmont, and on Mte. Somma, Italy; the Vilyuy River, Siberia; Christiansand, Nor.; Litchfield, Quebec; and Auburn, Maine, Amity, N.Y., and Franklin, N.J. For chemical formula and detailed physical properties, see silicate mineral (table)