igneous

Gabbro with Quartz Vein

Gabbro (mafic intrusive igneous rock)

Hardness: 6-7 (Mohs); Color: Dark grey to black matrix with white vein; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained); Specific Gravity: 2.7-3.3

Hardness: 6-7 (Mohs)
Color: Dark grey to black matrix with white vein
Luster: Dull to vitreous

Identified May 28, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs); Color: Dark grey to black matrix with white vein; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained); Specific Gravity: 2.7-3.3

Formation & geological history

Formed by the slow cooling of magnesium-rich and iron-rich magma beneath the Earth's surface. The white vein suggests a later hydrothermal event where silica-rich fluids filled a fracture and crystallized into quartz.

Uses & applications

Crushed stone for road construction, railroad ballast, and occasionally polished for use as 'black granite' countertops or cemetery markers.

Geological facts

Gabbro is the intrusive equivalent of basalt and makes up a large portion of the deep oceanic crust.

Field identification & locations

Identified by its dark color (mafic) and visible crystalline texture. It lacks the high silica content of granite. This specimen features a prominent mineral vein cutting through the primary rock body.

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