igneous
Gabbro
Gabbro (Mafic intrusive igneous rock)
Hardness: 6-7 (Mohs); Color: Dark grey, black, or dark green; Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained); Specific Gravity: 2.7-3.3.
- Hardness
- 6-7 (Mohs)
- Color
- Dark grey, black, or dark green
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark grey, black, or dark green; Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained); Specific Gravity: 2.7-3.3.
Formation & geological history
Formed by the slow cooling of magnesium-rich and iron-rich magma deep beneath the Earth's surface (intrusive). Often found in oceanic crust and large plutonic complexes.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as 'black granite' for countertops, floor tiles, and cemetery markers.
Geological facts
Gabbro is the intrusive equivalent of basalt. It is a major component of the deep oceanic crust, formed at mid-ocean ridges.
Field identification & locations
Identify by its dark color and coarse, interlocking crystals visible to the naked eye. Often found in mountainous regions or areas with exposed ancient oceanic crust.
