igneous
Gabbro
Gabbro
Hardness: 6-7 on Mohs scale; Color: Dark green, black, or dark gray; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.7-3.3.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark green, black, or dark gray
- Luster
- Vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark green, black, or dark gray; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); 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. It is the intrusive equivalent of basalt.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and concrete aggregate. High-quality varieties are used as Dimension Stone (black granite) for countertops and floor tiles.
Geological facts
Gabbro makes up a large part of the Earth's deep oceanic crust. It is often referred to as 'Black Granite' in the commercial decorative stone trade despite being geologically different from true granite.
Field identification & locations
Identify in the field by its dark color and coarse, interlocking crystals visible to the naked eye. Commonly found in large plutons or oceanic lithosphere. Look for its presence in mountain ranges where tectonic uplift has exposed deep crustal rocks.
