Formula: Ca2Al2Si3O10(OH)2

Species: Silicates – (Innosilicates)

Colour: Colourless to gray to yellow, yellow-green or white

Lustre: Vitreous, Pearly

Hardness: 6 – 6½

Specific Gravity: 2.8 – 2.95

Crystal System: Orthorhombic

Name: Named in 1788 by Abraham Gottlieb Werner in honor of the Dutch Colonel, Hendrik von/van Prehn (1733 -1785), who is credited with discovering the mineral in 1774 at the Cape of Good Hope in South Africa. Von Prehn was a governor of Cape of Good Hope (1779-1780) until he was dismissed. He was a naturalist and mineral collector who brought the first specimens of his namesake mineral to Europe. A considerable mystique and folklore have surrounded Prehn and prehnite. It has been claimed that prehnite was the first mineral named for a person.

Type Locality: Karoo dolerites, Cradock, Inxuba Yethemba Local Municipality, Chris Hani District Municipality, Eastern Cape – South Africa

The Al analogue of ferriprehnite. Both seem to belong to the prehnite group that also likely contains amstallite. A relatively common calcium alumosilicate occurring in low-temperature hydrothermal environments. Colourless brick-shaped crystals may be confused with stellerite.