igneous
Basalt
Fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene with possible olivine
AI-generated identification · may be incorrectDark gray, dull to slightly granular, dense, and fine-grained; typically Mohs 5–6, with no obvious cleavage and interlocking microscopic crystals. The specimen appears weathered and may contain minor vesicles or iron staining.
Identified More igneous →
Explore Basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, dull to slightly granular, dense, and fine-grained; typically Mohs 5–6, with no obvious cleavage and interlocking microscopic crystals. The specimen appears weathered and may contain minor vesicles or iron staining.
Formation & geological history
Forms when basaltic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and hotspot islands. Most examples range from recent to Precambrian in age; the image alone cannot establish a precise age.
Uses & applications
Widely used as crushed aggregate, road base, railway ballast, riprap, and building stone; attractive varieties are used for landscaping and polished objects. Ordinary hand specimens have modest collector value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the oceanic crust. It commonly weathers to reddish-brown iron oxides and can develop columnar jointing in thick flows.
Field identification & locations
Identify it by its charcoal-gray color, substantial weight, fine texture, and inability to scratch easily with a steel knife; a streak test is usually unavailable because it is hard. Common locations include volcanic regions, ocean islands, flood basalts, and river gravels derived from them.
