igneous
Weathered basalt (likely vesicular basalt)
Basalt; primarily plagioclase feldspar, pyroxene, and often olivine (approx. 45–52% SiO₂)
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to weakly vitreous luster, with pale weathering veins or alteration patches and a possible vesicle. Hardness is about 5–6 Mohs; massive, with poor cleavage and typical density of 2.8–3.0 g/cm³.
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Physical properties
Dark gray to black, fine-grained, dull to weakly vitreous luster, with pale weathering veins or alteration patches and a possible vesicle. Hardness is about 5–6 Mohs; massive, with poor cleavage and typical density of 2.8–3.0 g/cm³.
Formation & geological history
An extrusive mafic igneous rock formed when low-viscosity lava cooled rapidly at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. Its exact age cannot be determined from the image and may range from recent to billions of years.
Uses & applications
Used as crushed aggregate, road base, concrete stone, riprap, and building or paving material; attractive polished pieces are occasionally collected. Ordinary specimens generally have little commercial value.
Geological facts
The lighter cream-colored areas may be calcite, zeolite, feldspar, or weathering products filling cavities and fractures. Basalt commonly weathers to reddish-brown soils and can contain small olivine crystals.
Field identification & locations
Identify it by its dark, dense, fine-grained texture, lack of visible large crystals, and occasional gas cavities; a streak, hardness, and acid test can help distinguish it from slag or other dark rocks. Common worldwide, especially Hawaii, Iceland, India’s Deccan Traps, oceanic islands, and volcanic regions.
