igneous
Weathered basalt pebble
Basalt, a fine-grained mafic volcanic rock; likely containing plagioclase and pyroxene with weathering products
AI-generated identification · may be incorrectDark gray-green to brown, dull to weakly earthy luster, fine-grained and massive; Mohs hardness about 5–6, with no obvious cleavage and typically high density (about 2.8–3.0). The rounded shape and cavities suggest stream or beach abrasion and vesicular texture.
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Physical properties
Dark gray-green to brown, dull to weakly earthy luster, fine-grained and massive; Mohs hardness about 5–6, with no obvious cleavage and typically high density (about 2.8–3.0). The rounded shape and cavities suggest stream or beach abrasion and vesicular texture.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. Its exact age and locality cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, roadstone, riprap, railway ballast, and building stone; attractive polished pieces are occasionally used decoratively, but this specimen is not gem quality.
Geological facts
The greenish coloration may reflect chlorite, epidote, or other secondary minerals replacing the original basalt minerals during low-temperature alteration.
Field identification & locations
Look for a fine-grained dark matrix, substantial weight, lack of visible quartz, and possible tiny vesicles; a streak, hardness, density, and acid test would improve identification. Common worldwide, especially near volcanic regions and basaltic shorelines.
