metamorphic

Greenstone (probable altered basalt)

Chlorite–epidote–actinolite-rich greenschist; composition commonly derived from basalt

AI-generated identification · may be incorrect

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.

Identified September 7, 2026More metamorphic →

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At a glance

Common name: Greenstone (probable altered basalt)
Scientific name: Chlorite–epidote–actinolite-rich greenschist; composition commonly derived from basalt
Category: metamorphic
Identified: September 7, 2026
Method: Standard

AI Estimated Value

Approximately $1–$10 for a small common specimen; polished, locality-labeled, or mineralogically distinctive pieces may sell for $10–$50.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

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.