igneous
Gabbro
Phaneritic Mafic Plutonic Rock
AI-generated identification · may be incorrectHardness: 6-7 (Mohs); Color: Dark gray to black, often with greenish hues; Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: Two directions at nearly 90 degrees (pyroxene); Specific gravity: 2.7-3.3.
- Hardness
- 6-7 (Mohs)
- Color
- Dark gray to black, often with greenish hues
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark gray to black, often with greenish hues; Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: Two directions at nearly 90 degrees (pyroxene); Specific gravity: 2.7-3.3.
Formation & geological history
Formed by the slow cooling of magnesium-rich and iron-rich magma inside the Earth's crust. It is the plutonic equivalent of basalt, often found in oceanic crust and mid-ocean ridges.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and concrete aggregate. Sometimes used in the dimension stone industry as 'black granite' for countertops and floor tiles.
Geological facts
Gabbro is much more common than people realize because most of it lies deep beneath the ocean floor. It is primarily composed of calcium-rich plagioclase feldspar and pyroxene minerals.
Field identification & locations
Identify in the field by its dark color and coarse, visible mineral grains. Unlike basalt, which is fine-grained, gabbro's crystals are large enough to see without a lens. Often found in layered intrusions or ophiolite complexes.
