mineral

Prehnite

Prehnite - Ca2Al(AlSi3O10)(OH)2

Hardness: 6-6.5 on the Mohs scale. Color: Typically light green to yellow-green (as seen in the specimen). Luster: Vitreous to pearly. Crystal Structure: Orthorhombic. Cleavage: Good in one direction. Specific Gravity: 2.8 - 2.95.

Hardness: 6-6
Luster: Vitreous to pearly

Identified March 17, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary or hydrothermal mineral in cavities (vugs) of mafic volcanic rocks like basalt. It often occurs as a result of low-grade metamorphism or hydrothermal alteration of plagioclase feldspars.

Uses & applications

Used primarily as a gemstone for jewelry (cabochons and beads) and as a decorative stone. It is also a popular specimen for mineral collectors because of its unique botryoidal (grape-like) growth habit.

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 called 'Cape Emerald' due to its color and origin near the Cape of Good Hope.

Field identification & locations

Identify in the field by its distinct pale 'apple-green' color and its occurrence in volcanic bubbles or veins. Common locations include the Karoo dolerites of South Africa, the Paterson area of New Jersey (USA), and the Northern Territory of Australia.