igneous
Gabbro
Gabbro (Mafic Plutonic Rock)
Hardness: 6-7 on Mohs scale; Color: Dark grey, black, or dark green; Luster: Phaneritic (visible crystals), vitreous to dull; Crystal structure: Coarse-grained granular; Cleavage: Good in two directions (due to pyroxene); Specific gravity: 2.7 to 3.3
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey, black, or dark green
- Luster
- Phaneritic (visible crystals), vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey, black, or dark green; Luster: Phaneritic (visible crystals), vitreous to dull; Crystal structure: Coarse-grained granular; Cleavage: Good in two directions (due to pyroxene); Specific gravity: 2.7 to 3.3
Formation & geological history
Formed by the slow crystallization of magnesium-rich and iron-rich magma deep beneath the Earth's surface (plutonic). It is the intrusive equivalent to basalt and is often found in the lower oceanic crust.
Uses & applications
Used in the construction industry as 'black granite' for countertops, floor tiles, and facing stone; also crushed into aggregate for road base and railroad ballast.
Geological facts
Gabbro makes up a large portion of the deep oceanic crust. The name was given by the Italian geologist Christian Leopold von Buch after a town in the Tuscany region of Italy.
Field identification & locations
Identify by its dark color and coarse-grained texture where light-colored minerals (plagioclase) and dark minerals (pyroxene/olivine) are roughly equal in size. Commonly found in large igneous intrusions or ophiolite complexes.
