igneous
Dark mafic rock, likely basalt or gabbro
Basaltic rock; commonly plagioclase feldspar + pyroxene, with possible olivine and iron oxides
AI-generated identification · may be incorrectDark gray to black, fine- to medium-grained, dull to weakly glassy luster; typical hardness about 5–6 Mohs, no obvious cleavage, and specific gravity roughly 2.8–3.1. The image is insufficient to distinguish basalt from coarse-grained gabbro confidently.
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Physical properties
Dark gray to black, fine- to medium-grained, dull to weakly glassy luster; typical hardness about 5–6 Mohs, no obvious cleavage, and specific gravity roughly 2.8–3.1. The image is insufficient to distinguish basalt from coarse-grained gabbro confidently.
Formation & geological history
Forms from cooling iron- and magnesium-rich magma, commonly in volcanic lava flows or shallow intrusive bodies. Ages range from recent eruptions to Precambrian rocks billions of years old.
Uses & applications
Crushed basalt is used for aggregate, road metal, rail ballast, and construction stone; attractive polished pieces may be used decoratively.
Geological facts
Basalt is Earth’s most widespread volcanic rock and makes up much of the oceanic crust. Gabbro is its slower-cooled, coarse-grained intrusive equivalent.
Field identification & locations
Look for a dense, dark rock that is generally nonlayered and may attract weakly to strongly if magnetite-rich; a fresh broken surface is more diagnostic than weathered exterior. Common worldwide, especially volcanic regions and oceanic terrains.
