igneous
Gabbro
Gabbro (mafic intrusive rock)
Hardness: 6-7 (Mohs scale), Color: Dark gray to black (mafic), Luster: Dull to sub-metallic on fresh surfaces, Crystal Structure: Phaneritic (coarse-grained) holocrystalline, Cleavage: Prismatic (from pyroxene), Specific Gravity: 2.7-3.3
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark gray to black (mafic), Luster: Dull to sub-metallic on fresh surfaces, Crystal Structure: Phaneritic (coarse-grained) holocrystalline, Cleavage: Prismatic (from pyroxene), Specific Gravity: 2.7-3.3
Formation & geological history
Formed by the slow crystallization of magnesium-rich and iron-rich magma beneath the Earth's surface (intrusive). Often found in the lower oceanic crust and in large plutonic bodies on continents.
Uses & applications
Used as 'black granite' in construction for counter tops, floor tiles, and facing stone; also used as crushed stone for road base and railroad ballast.
Geological facts
Gabbro is the intrusive equivalent of basalt. It is a major component of the oceanic crust, found in ophiolite sequences where sections of the seafloor have been thrust onto land.
Field identification & locations
Identified in the field by its dark color and coarse, interlocking crystals of plagioclase feldspar and pyroxene. Found globally in mountainous regions and areas of ancient volcanic activity.
