metamorphic

Likely hornblende-rich amphibolite

Amphibolite, composed chiefly of hornblende (amphibole) and plagioclase feldspar

AI-generated identification · may be incorrect

Dark brown-gray, rough, fine- to medium-grained rock with scattered light mineral grains and no obvious layering. Hornblende has Mohs hardness 5–6; plagioclase about 6; exact properties cannot be confirmed from the image.

Identified September 28, 2026More metamorphic →

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Physical properties

Formation & geological history

Typically forms when basalt or gabbro is metamorphosed under moderate-to-high temperatures and pressures, commonly during mountain building. Its age cannot be determined from appearance alone.

Uses & applications

Amphibolite is used as crushed aggregate, road stone, and occasionally decorative building stone; this small, unpolished piece has little jewelry value.

Geological facts

Its dark color commonly comes from hornblende, while pale feldspar grains create the speckled appearance.

Field identification & locations

Look for a dense, dark rock with interlocking dark amphibole and pale feldspar grains; confirmatory identification may require examining a fresh surface or mineral tests. Amphibolite occurs in metamorphic belts worldwide.