igneous
Gabbro
Gabbro
AI-generated identification · may be incorrectHardness: 6-7 (Mohs). Color: Dark gray to black, often with greenish tint. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained). Specific gravity: 2.7-3.3. Major components: Plagioclase feldspar, pyroxene, and olivine.
- Hardness
- 6-7 (Mohs)
- Color
- Dark gray to black, often with greenish tint
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 (Mohs). Color: Dark gray to black, often with greenish tint. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained). Specific gravity: 2.7-3.3. Major components: Plagioclase feldspar, pyroxene, and olivine.
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 and is commonly found in oceanic crust and thick continental intrusions.
Uses & applications
Used as crushed stone for construction, railroad ballast, and road base. When polished, it is sold as 'black granite' for countertops, floor tiles, and grave markers.
Geological facts
Gabbro makes up much of the lower oceanic crust. It is denser than granite and lacks the quartz common in granitic rocks. Some gabbro deposits contain significant amounts of precious metals like platinum and chromium.
Field identification & locations
Identify in the field by its coarse, dark, 'salt and pepper' appearance without visible quartz. Found in mountainous or volcanic regions where deep-seated rocks have been uplifted. Collectors look for pieces with large pyroxene crystals.
