metamorphic
Weathered greenstone (likely serpentinite or altered basalt)
Serpentinite-group rock, commonly dominated by serpentine minerals (antigorite/lizardite); exact identification requires testing
AI-generated identification · may be incorrectPale olive-green, mottled, dull to waxy luster, fine-grained and brecciated-looking; typically Mohs 2.5–4, with no obvious cleavage. The rounded shape and surface cracking indicate strong weathering or stream abrasion.
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Physical properties
Pale olive-green, mottled, dull to waxy luster, fine-grained and brecciated-looking; typically Mohs 2.5–4, with no obvious cleavage. The rounded shape and surface cracking indicate strong weathering or stream abrasion.
Formation & geological history
Likely formed when ultramafic mantle rock was hydrothermally altered to serpentine, or when basalt underwent low-grade metamorphism; age depends on its source terrane. Common in ophiolites and tectonic suture zones.
Uses & applications
Serpentinite is used as decorative stone, aggregate, and occasionally carving material; specimens have modest collector interest. Avoid dust, since some serpentinite deposits may contain asbestos-forming minerals.
Geological facts
Greenstone is a field term and can include several rocks, so this identification is provisional. A white streak, low hardness, and possible magnetism would help distinguish serpentinite from altered basalt or chlorite-rich rock.
Field identification & locations
Common in California, Italy, New Zealand, Oman, the Appalachians, and other ophiolite belts. Test hardness against a fingernail or copper coin, inspect a fresh surface, and use a magnet; laboratory thin-section or XRD testing is definitive.
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