igneous
Weathered basaltic rock (likely basalt)
Basalt; primarily plagioclase feldspar, pyroxene, and possibly olivine, with surface alteration minerals
AI-generated identification · may be incorrectFine-grained, dark gray to brown, dull to slightly earthy luster, with mottled pale weathering and possible vesicles. Typical hardness is about 5–6 Mohs; cleavage is not visible in the whole rock and specific gravity is commonly 2.8–3.0.
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Physical properties
Fine-grained, dark gray to brown, dull to slightly earthy luster, with mottled pale weathering and possible vesicles. Typical hardness is about 5–6 Mohs; cleavage is not visible in the whole rock and specific gravity is commonly 2.8–3.0.
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. The specimen’s age cannot be determined from the photograph; its brown and pale surface reflects chemical weathering.
Uses & applications
Used widely as crushed aggregate, road base, railroad ballast, riprap, and dimension stone; attractive polished pieces may be used decoratively but this specimen is not gem-quality.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Pale patches may represent feldspar-rich areas, alteration, or attached weathering products rather than a separate mineral.
Field identification & locations
Identify by its dense, fine texture, dark color, heavy feel, and lack of obvious large crystals; a fresh broken surface should be dark gray. Common worldwide, especially Hawaii, Iceland, India, and oceanic terrains.
