igneous
Likely basalt or andesite fragments
Fine-grained volcanic rock, likely basalt (plagioclase and pyroxene, sometimes olivine); exact identification requires testing
AI-generated identification · may be incorrectDark gray to brown, dull and fine-grained with no visible crystals; typically Mohs hardness about 5–6, with a dense, interlocking crystalline texture and no prominent cleavage.
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Physical properties
Dark gray to brown, dull and fine-grained with no visible crystals; typically Mohs hardness about 5–6, with a dense, interlocking crystalline texture and no prominent cleavage.
Formation & geological history
Probably formed when lava cooled rapidly at or near Earth’s surface; volcanic rocks range widely in age, and the image cannot establish the specimen’s age.
Uses & applications
Commonly used as crushed aggregate for roads, concrete, and construction; these small rough fragments have little jewelry use.
Geological facts
Basalt is one of Earth’s most widespread volcanic rocks, but similar-looking andesite and other fine-grained rocks cannot be distinguished reliably from appearance alone.
Field identification & locations
A dark, compact rock with a fine, gritty-looking texture suggests basalt; a streak, hardness test, density, and fresh surface would help confirm it. Basalt occurs worldwide in volcanic regions and ancient lava flows.
