igneous
Dark basaltic rock, possibly vesicular basalt
Basalt; chiefly plagioclase feldspar, clinopyroxene, and commonly olivine or iron-titanium oxides
AI-generated identification · may be incorrectTypically dark gray to black, fine-grained, with a dull to slightly glassy luster; hardness about 6–7 Mohs, no prominent cleavage, and specific gravity roughly 2.8–3.0. The visible pale pits and irregular texture may indicate vesicles, weathering, or embedded mineral grains.
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Physical properties
Typically dark gray to black, fine-grained, with a dull to slightly glassy luster; hardness about 6–7 Mohs, no prominent cleavage, and specific gravity roughly 2.8–3.0. The visible pale pits and irregular texture may indicate vesicles, weathering, or embedded mineral grains.
Formation & geological history
An extrusive igneous rock formed when low-silica basaltic lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions. Its exact geological age cannot be determined from the image.
Uses & applications
Crushed basalt is used for aggregate, road base, concrete, riprap, and basalt fiber; attractive dense pieces may be used decoratively. Ordinary specimens generally have little collector value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. It can resemble black-and-gray andesite or industrial slag, so texture and density are useful for confirmation.
Field identification & locations
Look for a heavy, uniform dark rock with a fine crystalline texture, possible small vesicles, and no obvious manufactured surfaces; a streak, magnet response, and fresh fracture can help distinguish basalt from slag. Common locations include volcanic regions and oceanic crust.
