igneous
Gabbro
Gabbro (mafic intrusive igneous rock)
Hardness: 6-7 Mohs; Color: Dark grey, black, or dark green; Luster: Phaneritic (coarse-grained); Crystal Structure: Granular; Cleavage: Good in two directions (pyroxene/amphibole); Specific Gravity: 2.7-3.3
- Hardness
- 6-7 Mohs
- Color
- Dark grey, black, or dark green
- Luster
- Phaneritic (coarse-grained)
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey, black, or dark green; Luster: Phaneritic (coarse-grained); Crystal Structure: Granular; Cleavage: Good in two directions (pyroxene/amphibole); 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 (plutonic). It is the chemically equivalent intrusive counterpart to basalt.
Uses & applications
Used as 'black granite' for countertops, floor tiles, and grave markers. Frequently used as road base, railroad ballast, and concrete aggregate due to its durability.
Geological facts
Gabbro makes up much of the lower oceanic crust. It is often misidentified as granite, but unlike granite, it contains little to no quartz.
Field identification & locations
Identified by its dark color and coarse, interlocking crystals visible to the naked eye. Look for it in mountainous regions with exposed deep-crustal or oceanic tectonic plates (ophiolites).
