igneous
Gabbro
Plutonic mafic rock
Hardness: 6-7 (Mohs scale), Color: Dark gray to black (mafic), Luster: Phaneritic (medium to coarse crystalline), Crystal structure: Equigranular, Cleavage: Usually distinct in the component pyroxene and plagioclase, Specific Gravity: 2.7-3.3
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark gray to black (mafic), Luster: Phaneritic (medium to coarse crystalline), Crystal structure: Equigranular, Cleavage: Usually distinct in the component pyroxene and plagioclase, Specific Gravity: 2.7-3.3
Formation & geological history
Formed by the slow crystallization of magnesium-rich and iron-rich magma inside the Earth's crust. It is often found in the lower part of the oceanic crust during various geological eras including the Precambrian to Cenozoic.
Uses & applications
Used in construction as 'black granite' for countertops, floor tiles, and gravestones. Also used as crushed stone for road base material and railroad ballast.
Geological facts
Gabbro is the intrusive equivalent of basalt. It is essentially the same chemical composition as basalt but cooled much slower, allowing larger crystals to grow visible to the naked eye.
Field identification & locations
Identify in the field by its dark color and visible, interlocking crystals of pyroxene and dark plagioclase feldspar. Commonly found in large igneous provinces and mid-ocean ridges.
