igneous
Dark mafic igneous rock, likely basalt or gabbro
Basalt–gabbroic rock; chiefly plagioclase feldspar and pyroxene, possibly olivine and iron oxides
AI-generated identification · may be incorrectDark gray to black, speckled, massive, and dull to slightly vitreous; likely Mohs hardness 5–6, with weak or absent cleavage at the hand-specimen scale. The relatively coarse visible grains suggest gabbro, while a finer texture would indicate basalt.
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Physical properties
Dark gray to black, speckled, massive, and dull to slightly vitreous; likely Mohs hardness 5–6, with weak or absent cleavage at the hand-specimen scale. The relatively coarse visible grains suggest gabbro, while a finer texture would indicate basalt.
Formation & geological history
Formed from cooling iron- and magnesium-rich magma, either as rapidly cooled lava (basalt) or slowly crystallized underground magma (gabbro), generally in oceanic crust or volcanic provinces. Most examples are Phanerozoic, though similar rocks occur throughout geologic time.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, riprap, and dimension stone; attractive polished pieces may serve as decorative stone, but this specimen has little gem value.
Geological facts
Its dark color reflects abundant mafic minerals and relatively low quartz content. A magnet may show attraction if magnetite is present.
Field identification & locations
Identify by dark color, high density, interlocking crystals, and absence of obvious layering or abundant quartz; a close look with a hand lens distinguishes coarse gabbro from fine basalt. Common worldwide, especially oceanic crust and volcanic belts.
