igneous
Likely basaltic rock
Fine-grained basalt, possibly dolerite/diabase
AI-generated identification · may be incorrectDark brown-gray, massive, fine-grained, and likely mafic; dull to weakly vitreous luster with no obvious cleavage. Typical hardness is about 5–6 Mohs and specific gravity 2.8–3.1; the triangular form appears shaped or naturally fractured, so exact identification from the image is uncertain.
Identified More igneous →
Explore Likely basaltic rock in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark brown-gray, massive, fine-grained, and likely mafic; dull to weakly vitreous luster with no obvious cleavage. Typical hardness is about 5–6 Mohs and specific gravity 2.8–3.1; the triangular form appears shaped or naturally fractured, so exact identification from the image is uncertain.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, generally from Cenozoic to Precambrian volcanic activity. If the grains are coarser than they appear, it may instead be shallow-intrusive diabase.
Uses & applications
Used as crushed aggregate, road stone, riprap, railway ballast, paving, and occasionally decorative stone. Ordinary specimens have little jewelry value.
Geological facts
Its brown coloration may reflect weathering and oxidation of iron-bearing minerals. Basalt commonly contains plagioclase feldspar, pyroxene, and sometimes olivine or magnetite.
Field identification & locations
Look for a dense, dark rock with tiny interlocking crystals, no fizz in dilute hydrochloric acid, and possible attraction to a strong magnet from magnetite. Common worldwide in volcanic regions, oceanic crust, and flood-basalt provinces.
