mineral

Prehnite

Prehnite (Ca2Al2Si3O10(OH)2)

Hardness: 6-6.5 on Mohs scale; Color: Pale green to yellow-green, translucent to semi-transparent; 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, translucent to semi-transparent
Luster: Vitreous to pearly

Identified March 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral in cavities and veins of mafic volcanic rocks (basalt). It typically grows during low-grade metamorphism or hydrothermal activity within igneous host rocks. Many specimens date back to the Triassic or Jurassic periods.

Uses & applications

Primarily used as a gemstone for jewelry (cabochons and beads) and as a decorative mineral for mineral collectors. It is sometimes called 'Grape Jade' in the trade.

Geological facts

Prehnite was the first mineral to be named after an individual, Colonel Hendrik Von Prehn, who discovered it in South Africa in 1788. It often forms 'botryoidal' (grape-like) clusters that are highly prized by collectors.

Field identification & locations

Identify in the field by its distinct pale 'seafoam' green color, common association with minerals like epidote or quartz, and its brittle nature. Common locations include South Africa, Australia (Wave Hill), and the Paterson area of New Jersey, USA.