mineral

Prehnite

Prehnite (Ca2Al(AlSi3O10)(OH)2)

Hardness: 6-6.5 Mohs. Color: Pale green to yellow-green. Luster: Vitreous to pearly. Crystal system: Orthorhombic. Cleavage: Good in one direction. Specific gravity: 2.80-2.90.

Hardness: 6-6
Color: Pale green to yellow-green
Luster: Vitreous to pearly

Identified July 3, 2026More mineral →

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Physical properties

Hardness: 6-6.5 Mohs. Color: Pale green to yellow-green. Luster: Vitreous to pearly. Crystal system: Orthorhombic. Cleavage: Good in one direction. Specific gravity: 2.80-2.90.

Formation & geological history

Formed through hydrothermal processes in cavities and veins of mafic volcanic rocks (like basalt). It is a secondary mineral resulting from the alteration of calcic plagioclase feldspars.

Uses & applications

Used primarily as a gemstone for jewelry (cabochons and beads) and as a collector's mineral specimen. In the past, it was a minor source of calcium but has no significant industrial use.

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 'Grape Jade' when found in globular or botryoidal forms.

Field identification & locations

Look for its distinct 'oil-green' color and translucent, somewhat cloudy appearance. It is commonly found in basaltic quarries in New Jersey (USA), South Africa, Australia, and Scotland. Collectors look for 'epidote inclusions' which appear as dark needles inside the stone.