metamorphic

Banded amphibolite (probable)

Amphibolite, chiefly hornblende + plagioclase, with possible quartz/biotite

AI-generated identification · may be incorrect

Dark gray to black, medium- to coarse-grained, weakly foliated and compositionally banded; vitreous to dull luster. Typical hardness is about 5–6 (hornblende) and specific gravity ~2.9–3.3; cleavage is mainly inherited from amphibole.

Identified September 22, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when basaltic or gabbroic protoliths underwent medium- to high-grade metamorphism, commonly during mountain building; ages range from Archean to modern tectonic belts. The pale bands likely represent plagioclase-rich layers or quartz veins.

Uses & applications

Used locally as crushed aggregate, riprap, and dimension stone; attractive polished pieces are collected but are uncommon as gemstones. It may also be mistaken for dark gneiss or altered basalt.

Geological facts

Amphibolite records metamorphic conditions commonly around 500–750°C. White vein material may be quartz or carbonate, and its exact identity requires thin-section or X-ray analysis.

Field identification & locations

Identify it by its dense dark matrix, amphibole-rich texture, foliation/banding, and lack of vesicles; a streak test is usually pale gray. Common in metamorphic belts worldwide, including the Appalachians, Canadian Shield, Alps, and Precambrian terrains.