What is a pale green mineral occurring in crystalline aggregates having a botryoidal or mammillary structure, and rarely in distinct crystals. It is a hydrous silicate of alumina and lime called?

prehnite — A pale green mineral occurring in crystalline aggregates having a botryoidal or mammillary structure, and rarely in distinct crystals. It is a hydrous silicate of alumina and lime. (Webster's 1913.)

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