igneous
Gabbro
Gabbro
Phaneritic (coarse-grained) texture; Dark grey to black color; Hardness: 6-7 (Mohs); Luster: Vitreous to dull; Specific gravity: 2.7 to 3.3; Major minerals include plagioclase feldspar and pyroxene.
- Hardness
- 6-7 (Mohs)
- Luster
- Vitreous to dull
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Physical properties
Phaneritic (coarse-grained) texture; Dark grey to black color; Hardness: 6-7 (Mohs); Luster: Vitreous to dull; Specific gravity: 2.7 to 3.3; Major minerals include plagioclase feldspar and pyroxene.
Formation & geological history
Formed by the slow cooling of magnesium-rich and iron-rich magma inside the Earth's crust (intrusive). They are often found in oceanic crust and thick continental intrusions.
Uses & applications
Used as crushed stone for construction, road base, and railroad ballast. Larger slabs are often sold as 'black granite' for kitchen countertops and floor tiles.
Geological facts
Gabbro is the chemcial equivalent of basalt, but cooled much slower under the surface, allowing crystals to grow larger. It is the major constituent of the lower oceanic crust.
Field identification & locations
Identify by its dark color and visible interlocking crystals. It lacks the quartz found in granite. Common in mountainous regions and areas with ancient volcanic history.
