mineral

Tumbled prehnite

Prehnite, Ca₂Al(AlSi₃O₁₀)(OH)₂

AI-generated identification · may be incorrect

Pale green to yellow-green, translucent, vitreous to pearly luster, commonly botryoidal or massive; Mohs hardness 6–6.5, specific gravity about 2.8–2.9, with imperfect cleavage. The rounded shape indicates tumbling and polishing; dark inclusions may be epidote or chlorite.

Identified September 12, 2026More mineral →

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Physical properties

Formation & geological history

Forms as a low-temperature hydrothermal mineral in cavities and fractures of basalt, diabase, and other mafic volcanic rocks, commonly with zeolites and epidote. Most specimens formed during alteration of volcanic rocks, generally from Paleozoic to Cenozoic settings.

Uses & applications

Used primarily as a lapidary stone, cabochon, bead, and collector mineral; it has little industrial use. Attractive translucent material is valued in jewelry and decorative carvings.

Geological facts

Prehnite was the first mineral named after a person, Colonel Hendrik von Prehn, who collected it at the Cape of Good Hope. Its rounded, grape-like botryoidal aggregates are especially distinctive in rough specimens.

Field identification & locations

Identify it by its soft green color, translucent waxy-to-glassy appearance, and frequent dark needle or moss-like inclusions; test cautiously because similar jade, serpentine, and green chalcedony occur. Common sources include South Africa, Australia, India, China, and the United States.