igneous
Likely basalt (possibly vesicular basalt)
Basalt; chiefly plagioclase feldspar, clinopyroxene, and often olivine, with iron-titanium oxides
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to weakly vitreous, with possible tiny vesicles; hardness about 6 on the Mohs scale, no obvious cleavage, and specific gravity roughly 2.8–3.0. The specimen appears weathered and may contain subtle brown oxidation or glassy surfaces.
Identified More igneous →
Explore Likely basalt (possibly vesicular basalt) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to black, fine-grained, dull to weakly vitreous, with possible tiny vesicles; hardness about 6 on the Mohs scale, no obvious cleavage, and specific gravity roughly 2.8–3.0. The specimen appears weathered and may contain subtle brown oxidation or glassy surfaces.
Formation & geological history
An extrusive mafic igneous rock formed when low-silica basaltic lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions. Basalt forms from the Precambrian to the present day and is widespread in oceanic crust and continental volcanic fields.
Uses & applications
Used extensively as crushed aggregate, road base, riprap, railroad ballast, building stone, and basalt fiber; attractive polished pieces are occasionally used decoratively. This small rough specimen has little commercial value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Its dark color reflects abundant ferromagnesian minerals and iron-bearing oxides.
Field identification & locations
Common in Hawaii, Iceland, the Pacific Northwest, oceanic islands, and flood-basalt provinces worldwide; identify it by its dark dense fine-grained texture and resistance to scratching. A streak test, hand lens, and magnet check can help distinguish it from slag or dark sedimentary rock.
