igneous
Gabbro
Phaneritic Mafic Igneous Rock
Hardness: 6-7 (Mohs); Color: Dark grey to black with visible crystals of plagioclase and pyroxene; Luster: Vitreous to dull; Crystal structure: Phaneritic (medium to coarse-grained); Cleavage: Distinct in minerals; Specific gravity: 2.7-3.3.
- Hardness
- 6-7 (Mohs)
- Luster
- Vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark grey to black with visible crystals of plagioclase and pyroxene; Luster: Vitreous to dull; Crystal structure: Phaneritic (medium to coarse-grained); Cleavage: Distinct in minerals; 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). Commonly found in the lower parts of the oceanic crust and in large layered intrusions.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as 'black granite' for polished countertops, floor tiles, and cemetery markers.
Geological facts
Gabbro is the intrusive equivalent of basalt. It is a major component of the Earth's oceanic crust. Some layered gabbro intrusions contain significant deposits of chromium, nickel, and platinum group elements.
Field identification & locations
Identified in the field by its dark color and coarse-grained texture where individual crystals are visible to the naked eye. Found in mountainous or coastal areas with tectonic uplift. Look for the absence of quartz.
