metamorphic
Tumbled greenstone or serpentine pebble
Likely serpentinite, composed mainly of serpentine-group minerals (antigorite/lizardite); identification is uncertain from the image alone
AI-generated identification · may be incorrectPale green-gray, matte to waxy luster, rounded and naturally or artificially smoothed surface; hardness about 2.5–4 Mohs, generally massive with no visible crystal structure or cleavage, and specific gravity about 2.5–2.6.
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Physical properties
Pale green-gray, matte to waxy luster, rounded and naturally or artificially smoothed surface; hardness about 2.5–4 Mohs, generally massive with no visible crystal structure or cleavage, and specific gravity about 2.5–2.6.
Formation & geological history
Serpentinite forms when ultramafic mantle rocks chemically alter through hydration, commonly during plate subduction; most examples are Paleozoic to Mesozoic or younger, depending on locality.
Uses & applications
Used as carving stone, ornamental material, and occasionally jewelry or tumbled-stone material; this small specimen has modest decorative value.
Geological facts
The green color results from hydrated magnesium silicate minerals and may vary from pale gray-green to deep mottled green. It can resemble nephrite jade, but is usually softer and less fibrous.
Field identification & locations
Common in ophiolites and tectonic zones, including California, Italy, New Zealand, and the Appalachians. A steel knife may scratch it; a vinegar test is usually ineffective, while waxy feel and green streaking favor serpentine.
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