metamorphic
Greenstone / altered mafic rock
Likely chlorite–actinolite metabasalt (greenschist); exact identification requires testing
AI-generated identification · may be incorrectDark olive-green, fine-grained, weakly foliated and slightly glossy when wet, with no obvious crystals or cleavage. Likely Mohs hardness 5–6; luster ranges dull to subvitreous, and specific gravity is roughly 2.8–3.2.
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Physical properties
Dark olive-green, fine-grained, weakly foliated and slightly glossy when wet, with no obvious crystals or cleavage. Likely Mohs hardness 5–6; luster ranges dull to subvitreous, and specific gravity is roughly 2.8–3.2.
Formation & geological history
Probably basalt altered during low-grade metamorphism, commonly producing chlorite, actinolite, epidote, albite, and quartz; age depends on locality and may range from Precambrian to modern tectonic belts.
Uses & applications
Used locally as crushed aggregate, landscaping stone, and occasional carving material; attractive polished pieces may be sold as greenstone, though this specimen appears ordinary rather than gem quality.
Geological facts
“Greenstone” is a field and commercial term covering several green rocks, including metabasalt, serpentinite, and chlorite schist. The green color most commonly comes from chlorite, epidote, or actinolite.
Field identification & locations
Common in ancient volcanic belts, subduction zones, and metamorphic terrains worldwide. Check for a dark basaltic streak, non-acid reaction, magnetism, and hardness; a thin section or X-ray diffraction is needed for certainty.
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