igneous
Gabbro
Gabbro
Hardness: 6-7 (Mohs scale); Color: Dark green, dark gray, or black; Luster: Sub-metallic to vitreous; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions at roughly 90 degrees; Specific Gravity: 2.7 to 3.3.
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark green, dark gray, or black
- Luster
- Sub-metallic to vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark green, dark gray, or black; Luster: Sub-metallic to vitreous; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions at roughly 90 degrees; Specific Gravity: 2.7 to 3.3.
Formation & geological history
Formed from the slow cooling and crystallization of magnesium-rich and iron-rich magma beneath the Earth's surface (plutonic). It is the intrusive equivalent of basalt and is typically found in oceanic crust and large layered intrusions.
Uses & applications
Used in the construction industry as 'black granite' for countertops, floor tiles, and facing stone. Also used as crushed stone (road base) and railroad ballast due to its durability.
Geological facts
Gabbro makes up a large part of the Earth's deep oceanic crust. It is often chemically identical to basalt, only differing in grain size because it cools much slower underground.
Field identification & locations
Identify by its dark color, coarse-grained texture, and weight (higher density than granite). Commonly found in the Adirondack Mountains, the Palisades Sill, and near oceanic ridges.
