mineral

Prehnite

Prehnite, Ca2Al2Si3O10(OH)2

Hardness of 6-6.5 on the Mohs scale, pale green to yellow-green color, vitreous to pearly luster, orthorhombic crystal system, uneven fracture and poor cleavage, specific gravity of 2.80-2.90.

Identified August 2, 2026More mineral →

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Physical properties

Hardness of 6-6.5 on the Mohs scale, pale green to yellow-green color, vitreous to pearly luster, orthorhombic crystal system, uneven fracture and poor cleavage, specific gravity of 2.80-2.90.

Formation & geological history

Forms in hydrothermal veins and cavities in mafic volcanic rocks, often associated with zeolites, calcite, and datolite.

Uses & applications

Primarily used as a gemstone in jewelry, often cut into cabochons, and valued by mineral collectors.

Geological facts

Prehnite was the first mineral to be named after a military person, having been discovered in South Africa by Hendrik von Prehn in 1783.

Field identification & locations

Can be identified by its characteristic soft apple-green color, botryoidal habit, and pearly luster on cleavage surfaces. Found globally including South Africa, Australia, and the US.