igneous
Gabbro
Gabbro (mafic intrusive igneous rock)
Hardness: 6-7 Mohs; Color: Dark gray to black, often with greenish hues; Luster: Phaneritic (crystalline); Structure: Coarse-grained; Specific Gravity: 2.7–3.3
- Hardness
- 6-7 Mohs
- Color
- Dark gray to black, often with greenish hues
- Luster
- Phaneritic (crystalline)
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Physical properties
Hardness: 6-7 Mohs; Color: Dark gray to black, often with greenish hues; Luster: Phaneritic (crystalline); Structure: Coarse-grained; Specific Gravity: 2.7–3.3
Formation & geological history
Formed by the slow cooling of magnesium-rich and iron-rich magma inside the Earth's crust (intrusive). Commonly found in deep oceanic crust and large plutons.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as a polished dimension stone for kitchen countertops and floor tiles (often sold as 'black granite').
Geological facts
Gabbro is the intrusive equivalent of basalt; while they have the same chemical composition, gabbro cools slowly underground allowing large crystals to form.
Field identification & locations
Identifiable by its dark color and coarse, interlocking crystalline texture. Found in mountainous or volcanic regions where tectonic activity has uplifted deep-seated rocks.
