igneous
Gabbro
Coarse-grained Intrusive Mafic Igneous Rock
Hardness: 6-7 on Mohs scale. Color: Dark grey to greenish-black or black with visible crystalline grains. Luster: Vitreous to sub-metallic. Texture: Phaneritic (coarse-grained). Composition: Primarily calcium-rich plagioclase feldspar and pyroxene (augite), often with minor olivine or amphibole.
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark grey to greenish-black or black with visible crystalline grains. Luster: Vitreous to sub-metallic. Texture: Phaneritic (coarse-grained). Composition: Primarily calcium-rich plagioclase feldspar and pyroxene (augite), often with minor olivine or amphibole.
Formation & geological history
Forms from the slow cooling and crystallization of mafic magma deep below the Earth's surface at mid-ocean ridges, rift zones, or deep crustal intrusions.
Uses & applications
Widely used as crushed stone for road construction, concrete aggregate, ballast for railways, and polished as decorative dimension stone known commercially as 'black granite'.
Geological facts
Gabbro makes up a major portion of the oceanic crust beneath the thin layer of basalt. The lunar highlands and maria also contain significant amounts of gabbro.
Field identification & locations
Identified by its dark color combined with coarse, visible mineral grains of equal size. Commonly found along oceanic plate boundaries, ophiolite complexes, and large igneous intrusions worldwide.
