metamorphic

Weathered mafic metamorphic rock, likely amphibolite

Amphibolite; chiefly hornblende amphibole and plagioclase feldspar, with possible biotite, epidote, and quartz

AI-generated identification · may be incorrect

Dark gray-green, coarse to medium grained, weakly foliated, with a dull to slightly vitreous luster; typical hardness is about 5–6 Mohs and specific gravity 2.9–3.3. The image suggests amphibolite, though a definitive identification requires thin-section or mineral testing.

Identified September 22, 2026More metamorphic →

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At a glance

Common name: Weathered mafic metamorphic rock, likely amphibolite
Scientific name: Amphibolite; chiefly hornblende amphibole and plagioclase feldspar, with possible biotite, epidote, and quartz
Category: metamorphic
Identified: September 22, 2026
Method: Standard

AI Estimated Value

About $5–$25 for an ordinary hand specimen; $25–$100 if unusually fresh, foliated, or aesthetically attractive.

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

Usually forms when basalt or gabbro undergoes medium- to high-grade regional metamorphism during mountain building, commonly in Precambrian to Phanerozoic metamorphic belts.

Uses & applications

Used locally as crushed stone, road aggregate, riprap, and sometimes dimension stone; attractive specimens are collected but it is not generally a jewelry material.

Geological facts

Its characteristic amphibole-rich composition records metamorphism in the amphibolite facies, typically around 500–750°C. Foliation may develop from aligned hornblende crystals.

Field identification & locations

Look for a dense dark green-black rock with visible elongated amphibole grains, weak banding, and no obvious vesicles; it commonly occurs in metamorphic terrains and alongside schist or gneiss. A streak, hardness, magnetism, and acid test can help distinguish it from basalt or serpentinite.