igneous
Gabbro (likely olivine-bearing)
Coarse-grained mafic intrusive rock; chiefly plagioclase feldspar and pyroxene, possibly olivine
AI-generated identification · may be incorrectDark gray-green, granular, and weakly glistening from exposed crystal faces; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, no consistent cleavage as a whole, and specific gravity about 2.9–3.3.
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Physical properties
Dark gray-green, granular, and weakly glistening from exposed crystal faces; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, no consistent cleavage as a whole, and specific gravity about 2.9–3.3.
Formation & geological history
Slow cooling of magnesium- and iron-rich magma deep in Earth’s crust, producing large crystals; specimens may range from Precambrian to modern oceanic-crust age. The rounded form is likely water-worn.
Uses & applications
Used as crushed stone, road aggregate, railroad ballast, dimension stone, and occasionally polished decorative stone; generally low gem value.
Geological facts
Gabbro is the intrusive equivalent of basalt and commonly forms oceanic crust and layered igneous complexes. Greenish sparkle can indicate olivine or altered mafic minerals.
Field identification & locations
Identify by its dark, visibly crystalline texture, high density, and lack of glassy or vesicular surfaces; common in oceanic crust and mafic intrusive bodies worldwide, including Scotland, Norway, South Africa, and the United States.
