n. [ So called from the German Colonel Prehn, who first found it. ] (Min.) 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. [ 1913 Webster ]

a. (Chem.) Pertaining to, or designating, a tetrabasic acid of benzene obtained as a white crystalline substance; -- probably so called from the resemblance of the wartlike crystals to the mammillæ on the surface of prehnite. [ 1913 Webster ]