igneous
Gabbro
Gabbro; coarse-grained mafic intrusive rock dominated by plagioclase and pyroxene
AI-generated identification · may be incorrectDark gray to black, coarse crystalline, granular texture with pale plagioclase and dark pyroxene/amphibole; typically Mohs 6–7, vitreous to dull luster, no cleavage as a rock, and specific gravity about 2.7–3.3.
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Physical properties
Dark gray to black, coarse crystalline, granular texture with pale plagioclase and dark pyroxene/amphibole; typically Mohs 6–7, vitreous to dull luster, no cleavage as a rock, and specific gravity about 2.7–3.3.
Formation & geological history
Forms when mafic magma cools slowly deep within the crust, commonly in oceanic crust and layered intrusions; specimens may range from Precambrian to modern geologic ages.
Uses & applications
Used as crushed aggregate, road stone, dimension stone, countertops, monuments, and occasionally decorative stone; generally low collector value.
Geological facts
Gabbro is the intrusive equivalent of basalt and may contain olivine, magnetite, or ilmenite. Its coarse grains indicate slow underground cooling.
Field identification & locations
Identify by its dark, speckled, visibly crystalline texture and hardness; unlike basalt, individual crystals are readily visible. Common in oceanic crust and mafic plutons worldwide, including Norway, Scotland, South Africa, and the United States.
