igneous
Black basalt or dark volcanic rock fragment
Likely basalt, composed chiefly of plagioclase feldspar and pyroxene, with possible magnetite
AI-generated identification · may be incorrectFine-grained, dark gray to black, generally dull to weakly vitreous; hardness about 5–6 Mohs, massive texture, no obvious cleavage, and relatively high density (~2.8–3.1 g/cm³). The image is somewhat blurry, so exact identification is limited.
Identified More igneous →
Explore Black basalt or dark volcanic rock fragment in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine-grained, dark gray to black, generally dull to weakly vitreous; hardness about 5–6 Mohs, massive texture, no obvious cleavage, and relatively high density (~2.8–3.1 g/cm³). The image is somewhat blurry, so exact identification is limited.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic fields, and flood-basalt provinces. Specimen age cannot be determined from the image; basalt ranges from ancient Precambrian to modern.
Uses & applications
Used widely as crushed aggregate, roadstone, concrete material, building stone, and decorative landscaping rock; attractive polished pieces may be collected but usually have modest value.
Geological facts
Basalt is the most common volcanic rock and makes up much of the ocean floor. It may be weakly magnetic if it contains abundant magnetite.
Field identification & locations
Look for a uniformly fine-grained black surface, high density, and lack of visible large crystals; a streak, magnetism test, and fresh fracture help distinguish it from coal, slag, or shale. Common worldwide, especially volcanic regions.
