What is a grayish or whitish mineral occurring in orthorhombic, prismatic crystals, also in columnar masses. It is a silicate of alumina and lime, and is allied to epidote called?

zoisite — A grayish or whitish mineral occurring in orthorhombic, prismatic crystals, also in columnar masses. It is a silicate of alumina and lime, and is allied to epidote. (Webster's 1913.)

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