igneous
Gray volcanic rock, likely basalt
Basalt; primarily plagioclase feldspar, pyroxene, and minor olivine/iron oxides
AI-generated identification · may be incorrectFine-grained, dark gray, dull to slightly earthy luster, with no obvious large crystals; hardness about 6 on Mohs scale, massive texture, and typically specific gravity 2.8–3.0. The rough, rounded piece may show weathering or a thin vesicular/altered surface.
Identified More igneous →
Explore Gray 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, dull to slightly earthy luster, with no obvious large crystals; hardness about 6 on Mohs scale, massive texture, and typically specific gravity 2.8–3.0. The rough, rounded piece may show weathering or a thin vesicular/altered surface.
Formation & geological history
Basalt forms when low-silica mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic flows and oceanic crust. Most examples range from recent eruptions to rocks hundreds of millions of years old.
Uses & applications
Used as crushed aggregate, road base, railway ballast, building stone, and occasionally polished architectural material; ordinary hand specimens have little jewelry value.
Geological facts
Basalt is the most common volcanic rock and makes up much of the ocean floor. It commonly contains microscopic crystals, so its composition is usually identified by color, density, and geological context rather than visible grains.
Field identification & locations
Look for a dense, dark-gray to black rock with a fine texture that scratches glass but not steel easily; it may be weakly magnetic. Common localities include Hawaii, Iceland, the Deccan Traps, the Columbia River Basalt Group, and oceanic islands.
