metamorphic

Amphibolite

Hornblende amphibolite; chiefly hornblende and plagioclase feldspar

AI-generated identification · may be incorrect

Typically dark gray to black, fine- to medium-grained, with elongated amphibole crystals producing a fibrous or streaked texture; hardness about 5–6 Mohs, vitreous to dull luster, and weak cleavage inherited from hornblende. The rounded shape appears naturally weathered or water-worn.

Identified September 11, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when basaltic or gabbroic rocks undergo medium- to high-grade regional metamorphism, commonly during mountain building. Most examples are Precambrian to Paleozoic, though amphibolite forms in many geologic eras.

Uses & applications

Used as crushed stone, aggregate, road material, and occasionally dimension stone; attractive specimens are collected but generally have modest gem value.

Geological facts

Its dark elongated grains are commonly hornblende, while lighter streaks may be plagioclase. It commonly records intense metamorphic conditions within ancient continental crust.

Field identification & locations

Identify by its black-green color, dense weight, and aligned amphibole texture; it is commonly found in metamorphic belts worldwide, including Canada, Scandinavia, the Alps, and the northeastern United States. A streak test, hardness comparison, and thin-section examination provide confirmation.