Prehnite is a calcium alumosilicate that occurs in hydrothermal veins but is most often found as a vein or amygdule mineral in basalt. This mineral was originally discovered in South Africa by Hendrik von Prehn, for whom it was named. Prehnite ranges from colorless to grayish, yellowish green or white and has a vitreous, pearly lustre. A pink variety of Prehnite was discovered at Michigan’s Keweenaw Peninsula.
Chemical composition: Ca2Al2Si3O10(OH)2; Hardness: 6-6.5