igneous
Gabbro
Gabbro (Coarse-grained Mafic Igneous Rock)
Hardness: 6-6.5 on Mohs scale. Color: Dark gray to black, often with greenish or dark speckles. Luster: Vitreous to dull. Texture: Phaneritic (coarse-grained). Composition: Predominantly calcium-rich plagioclase feldspar and pyroxene (augite), with minor olivine or hornblende. Specific gravity: 2.8 - 3.1.
- Hardness
- 6-6
- Color
- Dark gray to black, often with greenish or dark speckles
- Luster
- Vitreous to dull
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: 6-6.5 on Mohs scale. Color: Dark gray to black, often with greenish or dark speckles. Luster: Vitreous to dull. Texture: Phaneritic (coarse-grained). Composition: Predominantly calcium-rich plagioclase feldspar and pyroxene (augite), with minor olivine or hornblende. Specific gravity: 2.8 - 3.1.
Formation & geological history
Formed by the slow cooling and crystallization of mafic magma deep within Earth's oceanic crust or intrusive plutons beneath volcanoes. Typically associated with oceanic crust and ophiolite complexes.
Uses & applications
Widely used as crushed stone for construction, road base, and concrete aggregate. High-quality dense varieties are polished and sold in the stone industry under the commercial trade name 'Black Granite' for countertops and monuments.
Geological facts
Gabbro is the intrusive chemical equivalent of basalt. While basalt cools quickly on the Earth's surface, gabbro cools slowly underground, allowing visible mineral crystals to develop.
Field identification & locations
Identified in the field by its dark color, heavy weight, and coarse-grained, interlocking crystal texture. Commonly found in oceanic crust exposures, mid-ocean ridge zones, and mountain belts worldwide. Minimal financial value as a single hand sample ($1-$5).
