igneous
Weathered basalt (likely vesicular basalt)
Basalt; chiefly plagioclase feldspar, pyroxene, and minor olivine/iron oxides
AI-generated identification · may be incorrectDark brown-black, fine-grained, dull to subtly glassy, with pale weathering or mineral-infill patches; typically massive and locally vesicular. Mohs hardness about 5–6; cleavage is not apparent; specific gravity roughly 2.8–3.1.
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Physical properties
Dark brown-black, fine-grained, dull to subtly glassy, with pale weathering or mineral-infill patches; typically massive and locally vesicular. Mohs hardness about 5–6; cleavage is not apparent; specific gravity roughly 2.8–3.1.
Formation & geological history
An extrusive mafic igneous rock formed when low-silica lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions from the Precambrian to present. The brown coloration and pale patches reflect surface weathering and alteration.
Uses & applications
Used as crushed aggregate, road base, riprap, ballast, and building stone; attractive polished pieces can serve as landscaping or educational specimens. Ordinary examples have little jewelry value.
Geological facts
Basalt is the most common volcanic rock and forms much of oceanic crust and many volcanic islands. Pale spots may be altered feldspar, zeolites, calcite, or other secondary minerals.
Field identification & locations
Identify by its heavy, dark, fine-grained appearance, lack of obvious quartz, and possible tiny gas cavities; a fresh broken surface should be darker than the weathered exterior. Common in volcanic regions worldwide, including Hawaii, Iceland, India, and the western United States.
