igneous
Basalt (likely vesicular basalt)
Basalt; primarily plagioclase feldspar, clinopyroxene, and olivine, with iron-titanium oxides
AI-generated identification · may be incorrectFine-grained, dark gray to black, commonly with brown weathering and small vesicles; dull to slightly glassy luster, interlocking crystal texture, Mohs hardness about 6, no prominent cleavage, specific gravity ~2.8–3.0.
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Physical properties
Fine-grained, dark gray to black, commonly with brown weathering and small vesicles; dull to slightly glassy luster, interlocking crystal texture, Mohs hardness about 6, no prominent cleavage, specific gravity ~2.8–3.0.
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. Its exact geological age cannot be determined from the photograph.
Uses & applications
Widely used as crushed aggregate, road base, railroad ballast, concrete aggregate, and building stone; attractive polished pieces are collected but are generally not jewelry gemstones.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the oceanic crust, including seafloor pillow lavas and large volcanic plateaus.
Field identification & locations
Identify it by its black, dense, fine-grained appearance, occasional gas cavities, and lack of visible large crystals; common worldwide in volcanic regions, including Hawaii, Iceland, India, and the Pacific Northwest.
