mineral
Prehnite
Ca2Al(AlSi3O10)(OH)2
Hardness of 6-6.5 on the Mohs scale, typically pale green to yellow-green or white, vitreous to pearly luster, crystal system is orthorhombic, uneven to conchoidal fracture, specific gravity of 2.80-2.95.
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Physical properties
Hardness of 6-6.5 on the Mohs scale, typically pale green to yellow-green or white, vitreous to pearly luster, crystal system is orthorhombic, uneven to conchoidal fracture, specific gravity of 2.80-2.95.
Formation & geological history
Forms as a secondary mineral in veins and cavities of mafic igneous rocks, such as basalt, through low-grade hydrothermal alteration.
Uses & applications
Used frequently as a gemstone in cabochons, carved ornaments, and collected as mineral specimens by enthusiasts.
Geological facts
Prehnite was the first mineral to be named after a military person, Dutch Colonel Hendrik von Prehn, who discovered it in South Africa in the 18th century.
Field identification & locations
Identified by its distinctive apple-green to yellow-green color, botryoidal or stalactitic habit, and association with zeolites. Common locations include South Africa, Australia, and the US (New Jersey).
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