igneous
Weathered dark volcanic rock, likely basalt
Basalt (plagioclase–pyroxene ± olivine), tentative identification
AI-generated identification · may be incorrectFine-grained, dark gray, dull to weakly granular surface with pale weathering patches; typically Mohs 5–6, massive, with no visible cleavage and specific gravity about 2.8–3.0. The image may show weathered or lichen-coated basalt, though texture is insufficient for certainty.
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Physical properties
Fine-grained, dark gray, dull to weakly granular surface with pale weathering patches; typically Mohs 5–6, massive, with no visible cleavage and specific gravity about 2.8–3.0. The image may show weathered or lichen-coated basalt, though texture is insufficient for certainty.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and flood-basalt provinces; ages range from modern eruptions to billions of years.
Uses & applications
Used extensively as crushed aggregate, road base, riprap, railway ballast, building stone, and occasionally as paving or architectural cladding; generally low specimen value.
Geological facts
Its dark color reflects abundant iron- and magnesium-rich minerals, while pale flecks may be plagioclase, alteration products, or surface deposits.
Field identification & locations
Look for a dense, fine-grained texture, dark color, and absence of obvious large crystals; a streak test is usually inconclusive, while a fresh broken surface and magnet response can help. Common worldwide, especially volcanic regions and oceanic terrains.
