igneous
Basalt (likely vesicular basalt)
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to faintly vitreous, with irregular fracture and possible small vesicles; hardness about 6 Mohs and specific gravity roughly 2.8–3.0. The apparent metallic sparkle may be minor reflective crystals or surface alteration.
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Physical properties
Dark gray to black, fine-grained, dull to faintly vitreous, with irregular fracture and possible small vesicles; hardness about 6 Mohs and specific gravity roughly 2.8–3.0. The apparent metallic sparkle may be minor reflective crystals or surface alteration.
Formation & geological history
An extrusive mafic igneous rock formed when low-silica lava cooled rapidly at or near Earth’s surface, commonly from volcanic eruptions and oceanic crust. The specimen’s exact geological age cannot be determined from the image.
Uses & applications
Widely used as crushed aggregate, road base, railroad ballast, riprap, and dimension stone; attractive polished varieties are used decoratively but are rarely jewelry gemstones.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the ocean floor, including mid-ocean ridges and large flood-basalt provinces.
Field identification & locations
Identify it by its uniformly dark, dense, fine-grained texture, lack of obvious layering, and possible gas bubbles; a hand lens and streak/acid tests help distinguish it from slag or meteorite. Common worldwide, especially volcanic regions and former oceanic terrains.
