igneous
Likely weathered basalt or basaltic rock
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to brown, fine-grained and dull, with irregular fracture and possible weathering rind; hardness about 5–6 Mohs, no obvious cleavage, and specific gravity roughly 2.8–3.0. The image is somewhat out of focus, so exact identification is uncertain.
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Physical properties
Dark gray to brown, fine-grained and dull, with irregular fracture and possible weathering rind; hardness about 5–6 Mohs, no obvious cleavage, and specific gravity roughly 2.8–3.0. The image is somewhat out of focus, so exact identification is uncertain.
Formation & geological history
An extrusive igneous rock formed when mafic lava rapidly cooled at or near Earth’s surface, commonly during volcanic eruptions. Basalt ranges from ancient Precambrian flows to modern lavas.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, riprap, building stone, and occasionally in landscaping or polished specimens; generally has little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the oceanic crust. Brown coloration commonly results from oxidation and surface weathering of iron-bearing minerals.
Field identification & locations
Look for a dense, dark, fine-grained texture, high weight, and absence of visible large crystals; a streak test is usually gray and weak. Common worldwide, especially Hawaii, Iceland, India’s Deccan Traps, and oceanic volcanic regions.
