mineral

Prehnite

Prehnite (Ca2Al(AlSi3O10)(OH)2)

Hardness: 6-6.5 on Mohs scale; Color: Pale green to yellow-green, sometimes white or colorless; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Cleavage: Good in one direction; Specific gravity: 2.80-2.95.

Hardness: 6-6
Color: Pale green to yellow-green, sometimes white or colorless
Luster: Vitreous to pearly

Identified June 27, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral in the cavities of mafic volcanic rocks (basalt) or through low-grade metamorphism. It often occurs as botryoidal (grape-like) clusters or masses.

Uses & applications

Primarily used as a gemstone for jewelry (cabochons and beads) and as a collector specimen. It is also historically notable as the first mineral named after a person.

Geological facts

It was named in 1788 after Colonel Hendrik Von Prehn, who discovered it in South Africa. In the gemstone trade, prehnite containing dark needle-like inclusions of Epidote or Black Tourmaline is highly sought after.

Field identification & locations

Identify by its 'soapy' or greasy feel and unique pale green, semi-translucent appearance often with dark inclusions. Common locations include South Africa, Australia, Mali, and the USA (New Jersey and Virginia).