igneous
Weathered basalt or other dark volcanic rock
Likely basalt; predominantly plagioclase feldspar and pyroxene, possibly olivine and iron oxides
AI-generated identification · may be incorrectDark brown-black, fine- to medium-grained, dull to slightly earthy luster, irregular fracture, and no obvious cleavage; estimated Mohs hardness 5–6 and specific gravity about 2.8–3.1. Strong weathering or staining obscures the original texture, so identification is provisional from the photograph.
Identified More igneous →
Explore Weathered basalt or other dark volcanic rock in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark brown-black, fine- to medium-grained, dull to slightly earthy luster, irregular fracture, and no obvious cleavage; estimated Mohs hardness 5–6 and specific gravity about 2.8–3.1. Strong weathering or staining obscures the original texture, so identification is provisional from the photograph.
Formation & geological history
Basalt forms when low-silica magma erupts and cools rapidly at or near Earth’s surface, commonly in lava flows and oceanic crust. Its age cannot be determined visually; it may range from very recent to billions of years old.
Uses & applications
Used as crushed aggregate, road metal, riprap, railway ballast, and occasionally dimension stone. Ordinary specimens have little jewelry value, though polished basalt can be decorative.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly contains microscopic crystals rather than visible ones.
Field identification & locations
Look for a dense, dark rock with tiny interlocking crystals, possible vesicles, and a black streak; a knife should not easily scratch fresh material. Common worldwide, especially volcanic regions and oceanic terrains.
