igneous
Mafic igneous rock, likely basalt or gabbro
Basalt–gabbro composition: chiefly plagioclase feldspar and pyroxene, with possible olivine and iron-titanium oxides
AI-generated identification · may be incorrectDark gray, dense, fine-to-medium crystalline, with dull to slightly vitreous luster; visible pale feldspar grains and metallic dark minerals. Hardness about 5–6 Mohs; no obvious cleavage at specimen scale; specific gravity commonly 2.8–3.1.
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Physical properties
Dark gray, dense, fine-to-medium crystalline, with dull to slightly vitreous luster; visible pale feldspar grains and metallic dark minerals. Hardness about 5–6 Mohs; no obvious cleavage at specimen scale; specific gravity commonly 2.8–3.1.
Formation & geological history
Formed from iron- and magnesium-rich magma. Fine-grained basalt crystallizes at or near the surface, whereas coarser gabbro crystallizes slowly underground; ages may range from recent volcanic rocks to Precambrian specimens.
Uses & applications
Used as crushed aggregate, roadstone, riprap, railroad ballast, and dimension stone; attractive polished pieces may be used decoratively.
Geological facts
The image suggests a mafic rock but cannot reliably distinguish basalt from fine-grained gabbro without examining grain size and texture closely.
Field identification & locations
Common in oceanic crust and volcanic regions, including Hawaii, Iceland, the Mid-Atlantic Ridge, and continental lava provinces. A streak test, fresh surface, grain-size inspection, and density check help identification; acid reaction should be absent.
