metamorphic
Greenstone (probable altered basalt)
Chlorite–epidote–actinolite-rich greenschist; composition commonly derived from basalt
AI-generated identification · may be incorrectFine-grained, dull to weakly waxy luster, mottled dark green with pale grains, and irregular fracture; typical hardness is about 5–6 Mohs and specific gravity about 2.8–3.2. The photograph is insufficient to confirm minerals or distinguish it from serpentine or green basalt.
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Physical properties
Fine-grained, dull to weakly waxy luster, mottled dark green with pale grains, and irregular fracture; typical hardness is about 5–6 Mohs and specific gravity about 2.8–3.2. The photograph is insufficient to confirm minerals or distinguish it from serpentine or green basalt.
Formation & geological history
Likely low-grade metamorphism of basalt in a hydrothermal or subduction-related setting, generally during the Paleozoic–Mesozoic or younger depending on locality. Similar greenstones occur in ancient oceanic crust and volcanic belts.
Uses & applications
Used locally as crushed aggregate, building stone, and occasionally ornamental material; attractive pieces may be cut or polished, though this specimen appears unpolished and small.
Geological facts
“Greenstone” is a field term rather than one mineral species; its color commonly comes from chlorite, epidote, actinolite, or serpentine. Greenschist-facies rocks form at relatively low temperatures and moderate pressures.
Field identification & locations
Check for a fine volcanic texture, green alteration minerals, hardness above common soapstone, and lack of obvious glass; a streak, acid, magnetism, and thin-section test would improve identification. Common in metamorphic belts worldwide, including the Appalachians, New England, New Zealand, and the Pacific Northwest.
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