igneous
Dark mafic igneous rock, likely basalt or gabbro
Basalt–gabbroic rock; mainly plagioclase feldspar and pyroxene, possibly olivine or magnetite
AI-generated identification · may be incorrectDark gray-brown, fine- to medium-grained, dull to slightly vitreous luster; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The image alone cannot reliably distinguish basalt from weathered gabbro.
Identified More igneous →
Explore Dark mafic igneous rock, likely basalt or gabbro in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-brown, fine- to medium-grained, dull to slightly vitreous luster; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The image alone cannot reliably distinguish basalt from weathered gabbro.
Formation & geological history
Formed when mafic magma cooled, rapidly at or near the surface as basalt or slowly underground as gabbro. Its exact age and geological setting are indeterminate from the photograph.
Uses & applications
Used as crushed aggregate, road stone, riprap, and occasionally building stone; attractive polished pieces may be collected but are generally low-value.
Geological facts
Mafic rocks are relatively rich in iron and magnesium and commonly appear dark because of pyroxene, olivine, and iron oxides.
Field identification & locations
Look for high density, dark color, and interlocking crystals; a streak test is usually inconclusive, while a fresh broken surface and hand lens help separate fine basalt from coarse gabbro. Common worldwide, especially in volcanic regions and oceanic crust.
