metamorphic

Banded amphibolite (likely hornblende schist)

Amphibolite; chiefly hornblende + plagioclase, with possible biotite and garnet

AI-generated identification · may be incorrect

Dark greenish-black, coarse-grained, foliated and strongly banded, with a dull to subvitreous luster. Typical hardness is 5–6 Mohs; crystals are mostly interlocking amphibole and feldspar, with no obvious cleavage on the specimen surface.

Identified August 15, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when basaltic or gabbroic rock underwent medium- to high-grade regional metamorphism, commonly during mountain building. Its exact geological age cannot be determined from the photograph and depends on the local bedrock.

Uses & applications

Used locally as crushed stone, riprap, aggregate, and occasionally dimension stone; attractive polished pieces are collectible but rarely gem-grade.

Geological facts

The dark mineral is commonly hornblende, whose two cleavage directions meet at about 60°/120°, while pale bands generally represent plagioclase-rich layers.

Field identification & locations

Look for a tough, heavy, dark rock with aligned amphibole crystals and alternating light-dark bands; it is commonly found in metamorphic belts worldwide, including the Appalachians, Canadian Shield, and Precambrian terrains.