metamorphic
Likely amphibolite
Amphibolite, composed mainly of hornblende (amphibole) and plagioclase feldspar
AI-generated identification · may be incorrectDark gray to black, coarse and crystalline with a subdued sheen; typical mineral hardness is about 5–6 Mohs. The image suggests interlocking dark and pale grains, but a photograph cannot confirm the minerals or rock type.
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Physical properties
Dark gray to black, coarse and crystalline with a subdued sheen; typical mineral hardness is about 5–6 Mohs. The image suggests interlocking dark and pale grains, but a photograph cannot confirm the minerals or rock type.
Formation & geological history
Usually forms when basaltic or gabbroic rock is metamorphosed under moderate-to-high heat and pressure. Such metamorphism occurs in many geological eras, commonly during mountain building.
Uses & applications
Used as crushed stone, road aggregate, and sometimes decorative facing stone; attractive pieces may be kept as specimens.
Geological facts
Amphibolite is named for its abundant amphibole minerals and can vary from strongly foliated to massive.
Field identification & locations
Look for a dense, dark rock with visible interlocking amphibole and feldspar grains; identification is best confirmed by examining a fresh surface and mineral grains. Amphibolite occurs in metamorphic belts worldwide.
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