igneous
Gabbro
Gabbro (mafic intrusive igneous rock)
Hardness: 6-7 Mohs; Color: Dark gray to black, often with greenish hues; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.7-3.3
- Hardness
- 6-7 Mohs
- Color
- Dark gray to black, often with greenish hues
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Dark gray to black, often with greenish hues; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); 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. It is the plutonic equivalent of basalt and is typically found in the lower oceanic crust.
Uses & applications
Used as 'black granite' for countertops, floor tiles, and grave markers. Also used as crushed stone (road base and railroad ballast) in construction.
Geological facts
Gabbro covers large sections of the ocean floor and is chemically equivalent to basalt. Some gabbro deposits contain significant concentrations of nickel, chromium, and platinum.
Field identification & locations
Identified in the field by its dark color and coarse, interlocking crystals of plagioclase feldspar and pyroxene. It is often found in mountainous regions where tectonic uplift has exposed oceanic crust.
