igneous
Gabbro (potentially weathered)
Mafic Plutonic Rock (Gabbro/Diabase)
Hardness: 6-7 (Mohs); Color: Dark grey, black, or dark green with brown iron-oxide staining; Luster: Dull to sub-vitreous; Structure: Phaneritic (visible crystals); Specific Gravity: 2.7-3.3
- Hardness
- 6-7 (Mohs)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark grey, black, or dark green with brown iron-oxide staining; Luster: Dull to sub-vitreous; Structure: Phaneritic (visible crystals); Specific Gravity: 2.7-3.3
Formation & geological history
Formed by the slow cooling of magnesium-rich and iron-rich magma deep beneath the Earth's surface. The location in Sudan (Bayuda Desert region) is known for the Neoproterozoic Bayuda Desert Complex containing various mafic igneous rocks.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as 'black granite' for countertops and headstones.
Geological facts
Gabbro is the intrusive equivalent of basalt and makes up much of the lower oceanic crust. It is often found in the roots of ancient mountain belts like the Arabian-Nubian Shield.
Field identification & locations
Identified by its dark color, coarse grain size, and high density. Look for visible lath-like plagioclase crystals and dark pyroxene. Common in the igneous basement complexes of northeastern Africa.
