metamorphic

Likely hornblende amphibolite fragment

Amphibolite, chiefly hornblende and plagioclase feldspar

AI-generated identification · may be incorrect

Dark green-black, granular to weakly foliated, with a dull to slightly vitreous luster; hornblende has Mohs hardness 5–6 and amphibolite typically has specific gravity about 2.9–3.3. The visible pale grains may be feldspar or weathered mineral inclusions.

Identified August 22, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when basaltic or gabbroic rock undergoes medium- to high-grade regional metamorphism, commonly during mountain building; specimens may range from Precambrian to geologically young metamorphic belts.

Uses & applications

Used locally as crushed aggregate, road stone, dimension stone, and occasionally as a dark decorative rock; small unattractive fragments generally have little commercial value.

Geological facts

Its elongate dark crystals and green-black color are characteristic of amphibole-rich metamorphic rock, though a photograph cannot confirm the identification or distinguish it confidently from altered basalt, diabase, or greenstone.

Field identification & locations

Common in metamorphic terrains worldwide, including the Appalachians, Scandinavia, and many Precambrian shields. A hand lens, streak, hardness test, and thin-section or X-ray analysis are useful for confirmation.