metamorphic
Likely amphibolite
Amphibolite, composed chiefly of hornblende and plagioclase
AI-generated identification · may be incorrectDark green to black, coarse- to medium-grained and speckled; typically Mohs 5–6, with a dull to weakly vitreous luster. Mineral grains are interlocking, and foliation may be subtle or absent.
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Physical properties
Dark green to black, coarse- to medium-grained and speckled; typically Mohs 5–6, with a dull to weakly vitreous luster. Mineral grains are interlocking, and foliation may be subtle or absent.
Formation & geological history
Forms when basaltic or gabbroic rocks undergo medium- to high-grade metamorphism, commonly during mountain-building; specimens can be of many geological ages.
Uses & applications
Used as crushed stone, aggregate, road material, and occasionally as a decorative building stone.
Geological facts
The image shows a dark, granular specimen consistent with amphibolite, though a photograph alone cannot confirm its mineral composition.
Field identification & locations
Look for dark green-black hornblende grains mixed with lighter plagioclase and a dense, hard texture; common in metamorphic belts worldwide. A hand lens and hardness or mineral tests can help distinguish it from other dark rocks.
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