igneous
Gabbro
Gabbro (Mafic Intrusive Igneous Rock)
Hardness: 6-7 (Mohs); Color: Dark gray to black, often with greenish tint; Luster: Phaneritic (medium to coarse-grained) and crystalline; Crystal structure: Orthorhombic/Monoclinic minerals; Specific Gravity: 2.7-3.3
- Hardness
- 6-7 (Mohs)
- Color
- Dark gray to black, often with greenish tint
- Luster
- Phaneritic (medium to coarse-grained) and crystalline
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark gray to black, often with greenish tint; Luster: Phaneritic (medium to coarse-grained) and crystalline; Crystal structure: Orthorhombic/Monoclinic minerals; 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 found in oceanic crust and mid-ocean ridges.
Uses & applications
Used in construction as 'black granite' for countertops, floor tiles, and as crushed stone for road base and railroad ballast.
Geological facts
Gabbro is the intrusive equivalent of basalt; while they have same chemical composition, basalt cools quickly on the surface and gabbro cools slowly underground.
Field identification & locations
Identify by its dark color and visible interlocking crystals. Common in mountain ranges and near ancient tectonic plate boundaries. Collectors look for phaneritic textures.
