metamorphic

Banded amphibolite (likely hornblende gneiss)

Amphibolite; primarily hornblende amphibole and plagioclase feldspar, commonly with biotite and quartz

AI-generated identification · may be incorrect

Typically dark green-black to gray, with strong light–dark banding and a granular to foliated texture; hornblende has Mohs hardness 5–6, plagioclase 6–6.5, subvitreous to pearly luster, and no prominent cleavage at the hand-specimen scale.…

Identified September 2, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when basaltic or gabbroic protoliths undergo medium- to high-grade regional metamorphism, commonly during mountain building; many examples are Precambrian to Paleozoic, though amphibolite can form at any age. The banding reflects metamorphic segregation and inherited layering or deformation.

Uses & applications

Used as crushed stone, aggregate, road material, and occasionally dimension stone; attractive banded pieces are sold as lapidary or decorative specimens but are not generally valuable gemstones.

Geological facts

Commonly contains elongated amphibole crystals aligned by foliation, producing a tough, splintery rock. It may resemble banded gneiss, but amphibolite is usually darker and richer in green-black amphibole.

Field identification & locations

Look for high density, dark green-black amphibole, pale feldspar bands, and a hard, foliated texture; a streak, hardness, and thin-section test can distinguish it from serpentinite or chlorite schist. Common in metamorphic belts worldwide, including Scandinavia, the Alps, Canada, and the Appalachian Mountains.