igneous
Small dark volcanic rock, likely basalt
Basalt; chiefly plagioclase feldspar, clinopyroxene, and minor olivine or iron-titanium oxides
AI-generated identification · may be incorrectFine-grained, dark gray to brown, dull to slightly glassy; Mohs hardness about 5–6, generally massive with no visible cleavage, and specific gravity about 2.8–3.0. The specimen appears weathered and vesicle-free, though the image limits identification.
Identified More igneous →
Explore Small dark volcanic rock, likely basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine-grained, dark gray to brown, dull to slightly glassy; Mohs hardness about 5–6, generally massive with no visible cleavage, and specific gravity about 2.8–3.0. The specimen appears weathered and vesicle-free, though the image limits identification.
Formation & geological history
Basalt forms when low-silica, iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and shield volcanoes. It can range from ancient Precambrian flows to modern eruptions.
Uses & applications
Widely used as crushed aggregate, road base, riprap, railway ballast, and building stone; attractive polished varieties are used decoratively. This small, ordinary fragment has minimal commercial value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the oceanic crust. It commonly forms columnar joints when thick lava flows cool and contract.
Field identification & locations
Identify it by its dark color, fine texture, heavy feel, and lack of obvious individual crystals; a streak test is usually gray, and it does not fizz with dilute hydrochloric acid. Common worldwide, especially Hawaii, Iceland, India’s Deccan Traps, and ocean-floor exposures.
