igneous
Gabbro
Gabbro
Hardness: 6-7 Mohs; Color: Dark grey, black, or dark green; Luster: Pearly to dull; Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions (due to pyroxene); Specific Gravity: 2.7-3.3
- Hardness
- 6-7 Mohs
- Color
- Dark grey, black, or dark green
- Luster
- Pearly to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey, black, or dark green; Luster: Pearly to dull; Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions (due to pyroxene); 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. It is the intrusive equivalent of basalt and is often found in the deep oceanic crust.
Uses & applications
Used as a construction material for roads (crushed stone), as dimension stone for kitchen countertops (often sold as 'black granite'), and as railroad ballast.
Geological facts
Gabbro covers much of the Earth's deep ocean floor. It is named after the town of Gabbro in Tuscany, Italy, where it was first studied. It can sometimes contain valuable minerals like nickel, chromium, and platinum.
Field identification & locations
Look for a dark-colored, heavy rock with clearly visible interlocking crystals. Unlike granite, it lacks significant quartz. It is commonly found in mountainous regions near fault lines or in ophiolite complexes.
