metamorphic

Likely amphibolite

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

AI-generated identification · may be incorrect

Coarse, irregularly crystalline rock with dark green-black and pale gray-brown minerals. Hornblende has Mohs hardness about 5–6 and vitreous to dull luster; plagioclase is about 6–6.5. The photo alone does not show enough detail to confirm the identification or crystal structure.

Identified September 26, 2026More metamorphic →

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Physical properties

Formation & geological history

Typically forms when basalt or gabbro is metamorphosed under medium- to high-grade heat and pressure, commonly during mountain building. Its age depends on the local geological history and cannot be determined from the image.

Uses & applications

Used as crushed stone and aggregate; attractive, durable pieces may be polished for decorative stone or collected.

Geological facts

Amphibolite is named for its common amphibole minerals, especially hornblende. Similar-looking dark, mottled rocks can include gneiss, diorite, or other mafic rocks.

Field identification & locations

The coarse dark-and-light mineral mixture is consistent with amphibolite, but identification would benefit from a fresh surface and mineral inspection. It occurs in metamorphic belts worldwide; check for elongated dark amphibole crystals and feldspar.