igneous
Gabbro
Gabbro
Hardness: 6-7 on the Mohs scale; Color: Dark green, gray, to black; Luster: Phaneritic (crystalline) and somewhat dull to sub-metallic; Crystal Structure: Coarse-grained; Cleavage: Two directions at nearly 90 degrees (pyroxene); Specific Gravity: 2.7-3.3
- Hardness
- 6-7 on the Mohs scale
- Color
- Dark green, gray, to black
- Luster
- Phaneritic (crystalline) and somewhat dull to sub-metallic
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Physical properties
Hardness: 6-7 on the Mohs scale; Color: Dark green, gray, to black; Luster: Phaneritic (crystalline) and somewhat dull to sub-metallic; Crystal Structure: Coarse-grained; Cleavage: Two directions at nearly 90 degrees (pyroxene); Specific Gravity: 2.7-3.3
Formation & geological history
Formed from the slow cooling of magnesium-rich and iron-rich magma deep beneath the Earth's surface (intrusive). They are often associated with mid-ocean ridges or ancient mountain-building events.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and concrete aggregate. High-quality slabs are polished and sold as 'Black Granite' for kitchen countertops and floor tiles.
Geological facts
Gabbro is the intrusive equivalent of basalt; both have the same chemical composition but different crystal sizes. It makes up a significant portion of the deep oceanic crust.
Field identification & locations
Identify in the field by its dark color and coarse, visible interlocking crystals of plagioclase feldspar and pyroxene. It lacks the quartz typically found in granite. Commonly found in large plutons or ophiolite complexes.
