igneous
Dark fine-grained rock fragment
Likely basalt or basaltic scoria; exact identification requires testing
AI-generated identification · may be incorrectDark gray-brown, dull to slightly granular, fine-grained and irregularly rounded; likely composed mainly of plagioclase, pyroxene, and possibly olivine. Estimated Mohs hardness 5–6; cleavage is not visible and specific gravity is likely about 2.7–3.0.
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Physical properties
Dark gray-brown, dull to slightly granular, fine-grained and irregularly rounded; likely composed mainly of plagioclase, pyroxene, and possibly olivine. Estimated Mohs hardness 5–6; cleavage is not visible and specific gravity is likely about 2.7–3.0.
Formation & geological history
Probably volcanic basalt formed from rapidly cooled mafic lava, generally younger than Earth’s crustal rocks and potentially ranging from ancient to modern eruptions. The image is insufficient to distinguish dense basalt from vesicular scoria or weathered slag.
Uses & applications
Common basalt is used as aggregate, road base, ballast, building stone, and occasionally landscaping material; this small fragment has negligible commercial or jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. Its dark color reflects abundant iron- and magnesium-rich minerals.
Field identification & locations
Look for a uniformly dark, hard surface, tiny crystals, and possible gas vesicles; a streak test, magnet test, density, and close inspection can help separate basalt from industrial slag. Common worldwide, especially volcanic regions and oceanic islands.
