mineral

Prehnite

Prehnite Ca2Al2Si3O10(OH)2

Hardness: 6-6.5 on Mohs scale; Color: Pale green to yellow-green, sometimes colorless or white; 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 colorless or white
Luster: Vitreous to pearly

Identified March 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral in hydrothermal cavities of mafic igneous rocks (volcanic basalt and diabase). It can also occur in low-grade metamorphic rocks. Geological age varies by the host rock, but it is often found in Mesozoic Era basalt flows.

Uses & applications

Primary use is as a gemstone for jewelry (beads, cabochons) and as a collector's mineral specimen. In the past, it was also studied for its unusual habit of forming 'grape-like' (botryoidal) clusters.

Geological facts

Prehnite was the first mineral to be named after a person—Colonel Hendrik von Prehn, who discovered it in South Africa in 1788. It is sometimes referred to as 'Cape Chrysolite' or 'Grape Jade' due to its appearance.

Field identification & locations

Identify by its distinct oily lustre, pale green 'menthol' color, and translucent to pearly appearance. It is commonly found in the Karoo dolerites of South Africa, the Paterson region of New Jersey, USA, and the Wave Hill station in Australia. Collectors should look for its common globule or botryoidal forms.