Source : Webster's Revised Unabridged Dictionary (1913)

Prehnite \Prehn"ite\, 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.