metamorphic
Greenstone (likely serpentinite or chlorite-rich metamorphic rock)
Probable serpentinite/chlorite schist; commonly dominated by serpentine-group minerals, chlorite, talc, and magnetite
AI-generated identification · may be incorrectTypically olive to gray-green, mottled, fine-grained, and waxy to dull with sparse pale veins; hardness about 2.5–4 Mohs, massive to weakly foliated, with no obvious cleavage. The rounded, polished surface obscures original texture.
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Physical properties
Typically olive to gray-green, mottled, fine-grained, and waxy to dull with sparse pale veins; hardness about 2.5–4 Mohs, massive to weakly foliated, with no obvious cleavage. The rounded, polished surface obscures original texture.
Formation & geological history
Formed by hydrothermal alteration of ultramafic mantle rocks, commonly during oceanic crust formation or tectonic metamorphism; ages range from Paleozoic to modern tectonic settings. Exact identification requires testing or thin-section analysis.
Uses & applications
Used as decorative stone, carvings, cabochons, landscaping material, and occasionally aggregate; attractive pieces have modest lapidary value.
Geological facts
“Greenstone” is a field term covering several green rocks, including serpentinite, chlorite schist, epidote-rich rocks, and altered basalt. Some serpentinite contains fibrous asbestos minerals and should not be cut or powdered without proper safety controls.
Field identification & locations
Common in ophiolite belts, subduction zones, and metamorphic terrains. Look for a green mottled color, soft-to-moderate hardness, waxy feel, white veins, and possible magnetism; a streak, hardness, magnet, and specific-gravity test would improve identification.
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