The Probert Encyclopaedia of Rocks & Minerals

PREHNITE

Prehnite is a mineral named after Colonel Hendrick Von Prehn who first discovered it at the Cape of Good Hope in South Africa. It was confirmed as a distinct species of mineral in 1788. Prehnite is a hydrous silicate of calcium and aluminium with the formulae Ca2Al2Si3O10(OH)2 and a relative hardness of 6 to 7. Prehnite occurs as a crusty lining in cavities in basalt and related rocks and is associated with zeolites, datolite, pectolite, and calcite. Prehnite has a characteristic green colour. Resembles hemimorphite but is of a lower specific gravity and fuses easily.
Research Prehnite