igneous
Basalt
Mafic volcanic rock, chiefly plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectTypically dark gray to black, fine-grained, with dull to slightly glassy luster; Mohs hardness about 6, no prominent cleavage as a rock, and specific gravity roughly 2.8–3.0. The specimen appears dense and fine-grained, though the image cannot confirm its exact mineral texture.
Identified More igneous →
Explore Basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically dark gray to black, fine-grained, with dull to slightly glassy luster; Mohs hardness about 6, no prominent cleavage as a rock, and specific gravity roughly 2.8–3.0. The specimen appears dense and fine-grained, though the image cannot confirm its exact mineral texture.
Formation & geological history
Forms when basaltic lava cools rapidly at or near Earth’s surface, commonly in the Cenozoic and older volcanic terrains; oceanic crust is predominantly basaltic. Individual specimens may be millions to billions of years old.
Uses & applications
Used extensively as crushed aggregate, road base, railway ballast, concrete aggregate, and dimension stone; attractive polished varieties are used decoratively. Common specimens generally have little commercial collector value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. It may contain vesicles, olivine crystals, or magnetic iron minerals.
Field identification & locations
Identify it by its black, heavy, fine-grained appearance, lack of visible large crystals, and possible attraction to a magnet; distinguish it from granite by its darker color and finer texture. Common worldwide, especially Hawaii, Iceland, oceanic islands, and volcanic provinces.
