igneous
Gabbro
Gabbro (mafic intrusive igneous rock)
Hardness: 6-7 (Mohs scale); Color: Dark grey, black, or dark green; Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.7-3.3
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey, black, or dark green
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey, black, or dark green; Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.7-3.3
Formation & geological history
Formed from the slow cooling of magnesium-rich and iron-rich magma deep beneath the Earth's surface. Often found in oceanic crust and large intrusive bodies.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and concrete aggregate. Specifically high-quality varieties are sold as 'Black Granite' for countertops and cemetery markers.
Geological facts
Gabbro is the chemical equivalent of basalt, but because it cools underground, it has much larger crystals. It is a major component of the lower oceanic crust.
Field identification & locations
Identify by its dark color and coarse, interlocking crystals that are visible to the naked eye. Commonly found in mountainous regions or areas with exposed ancient oceanic crust.
