mineral

Tumbled prehnite (probable)

Prehnite, Ca₂Al(AlSi₃O₁₀)(OH)₂

AI-generated identification · may be incorrect

Pale yellow-green, translucent, vitreous to waxy luster, typically massive rather than visibly crystalline; Mohs hardness 6–6.5, specific gravity about 2.8–2.9, with imperfect cleavage. The rounded shape indicates human tumbling and polishing.

Identified September 18, 2026More mineral →

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Physical properties

Formation & geological history

Prehnite forms in cavities and fractures of basaltic volcanic rocks through low-temperature hydrothermal alteration, commonly associated with zeolites, epidote, and quartz. Most specimens are Cenozoic to older, depending on the host volcanic rock.

Uses & applications

Used mainly as a lapidary and collector stone; attractive transparent pieces may be cut as cabochons, while common material is sold as tumbled stone.

Geological facts

Its green color comes from iron substitution; yellow, gray, and colorless varieties occur. The image could also represent pale-green chalcedony or glass, so identification is provisional without testing.

Field identification & locations

Check for a waxy/vitreous luster, moderate hardness, and density; it should scratch glass but not quartz. Common sources include South Africa, Australia, India, China, and the United States.