mineral

Prehnite

Prehnite - Ca2Al(AlSi3O10)(OH)2

Hardness: 6.0-6.5 on Mohs scale; Color: typically pale green to oil green, sometimes yellow or white; Luster: Vitreous to pearly; Crystal structure: Orthorhombic (often occurs in botryoidal or globular aggregates); Cleavage: Good in one direction; Specific gravity: 2.80-2.95.

Hardness: 6
Color: typically pale green to oil green, sometimes yellow or white
Luster: Vitreous to pearly

Identified March 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed through low-grade metamorphism or hydrothermal activity. It is typically found lining cavities and fractures in volcanic rocks (specifically basalt), often associated with zeolites. Formation can occur over millions of years as hydrothermal fluids cool within rock voids.

Uses & applications

Used primarily as a gemstone for jewelry (cabochons and beads) and as a popular mineral specimen for collectors. In some cases, it has been used as a minor decorative stone.

Geological facts

It 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 'fingers' or grape-like clusters known as botryoidal growth. It is sometimes called 'Grape Jade' by collectors.

Field identification & locations

Identify in the field by its distinct pale-green color and 'bumpy' or globular (botryoidal) appearance within basaltic cavities. It is commonly found in South Africa, Australia, Scotland, and the Paterson area of New Jersey, USA. Unlike quartz, it has a slightly oily or pearly luster and a distinct pear-green shade.