igneous
Gabbro
Gabbro
Hardness: 6-7 (Mohs scale); Color: Dark grey, black, or dark green; Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: Prominent in two directions; Specific gravity: 2.7 - 3.3.
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey, black, or dark green
- Luster
- Dull to sub-vitreous
Identified More igneous →
Explore Gabbro in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey, black, or dark green; Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: Prominent in two directions; 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). Often found in oceanic crust and thick continental intrusions.
Uses & applications
Used primarily in the construction industry as crushed stone (road base, railroad ballast) and sometimes polished for use as dimension stone, known commercially as "black granite" in countertops.
Geological facts
Gabbro is the chemical equivalent of basalt, but basalt is extrusive (fine-grained) while gabbro is intrusive (coarse-grained). It makes up a large portion of the deep oceanic crust.
Field identification & locations
Identify by its dark color and coarse, interlocking crystals visible to the naked eye. Found in Ophiolite complexes or large layered intrusions like the Duluth Complex in Minnesota.
