igneous
Gabbro
Gabbro
Hardness: 6-6.5 on the Mohs scale. Color: Dark gray to greenish-black with medium-to-coarse phaneritic grain texture. Luster: Vitreous to dull. Mineral composition: Mainly calcium-rich plagioclase feldspar, pyroxene (augite), and minor olivine or amphibole.
- Hardness
- 6-6
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-6.5 on the Mohs scale. Color: Dark gray to greenish-black with medium-to-coarse phaneritic grain texture. Luster: Vitreous to dull. Mineral composition: Mainly calcium-rich plagioclase feldspar, pyroxene (augite), and minor olivine or amphibole.
Formation & geological history
Formed through the slow cooling and crystallization of mafic magma deep below the Earth's surface (intrusive igneous rock). It is the plutonic equivalent of basalt, often found in oceanic crust and layered intrusive complexes.
Uses & applications
Used widely as crushed stone for construction, road base material, ballast, and as a durable decorative dimension stone commercially sold under the trade name 'black granite'.
Geological facts
Gabbro makes up a major portion of the Earth's oceanic crust beneath the thin layer of basalt. Some layered gabbro intrusions contain significant deposits of platinum-group elements, nickel, copper, and titanium.
Field identification & locations
Identified in the field by its dark color, heavy weight (high density), and coarse-grained, interlocking crystalline texture showing light-colored plagioclase mixed with dark pyroxene. Common in riverbeds, glacial deposits, and mountain roots.
