metamorphic

Amphibolite

Hornblende–plagioclase amphibolite

AI-generated identification · may be incorrect

Typically dark green-black, medium- to coarse-grained, with a dull to weakly vitreous luster and massive or weakly foliated texture. Hardness is about 5.5–6.5; composition is dominated by hornblende amphibole and plagioclase, with possible biotite, epidote, quartz, and magnetite.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when basaltic or gabbroic protoliths undergo medium- to high-grade metamorphism, commonly during mountain building; many examples are Precambrian to Paleozoic, though age depends on locality.

Uses & applications

Used locally as crushed aggregate, road stone, and dimension stone; attractive polished pieces are collected but are generally not a major gemstone material.

Geological facts

Its green-black color reflects iron- and magnesium-rich amphibole, while pale streaks may represent plagioclase or quartz. It can resemble hornblende gneiss, greenstone, or serpentinite.

Field identification & locations

Identify it by its dense dark-green appearance, interlocking crystals, amphibole’s elongated cleavage surfaces, and lack of vesicles or glassy texture; common in metamorphic belts worldwide, including Canada, the northeastern United States, Scandinavia, and the Alps.