igneous
Gabbro Pebble
Gabbro (intrusive mafic rock)
Hardness: 6-7 on Mohs scale; Color: Dark green, black, and gray mottling; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.7-3.3.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark green, black, and gray mottling
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark green, black, and gray mottling; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); 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. Often found in oceanic crust and mid-ocean ridges.
Uses & applications
Commonly used as crushed stone for road construction, railroad ballast, and occasionally polished for use as 'black granite' in countertops and grave markers.
Geological facts
Gabbro is the intrusive equivalent of basalt. It is a major component of the lower oceanic crust and is often associated with ore deposits of nickel, chromium, and platinum.
Field identification & locations
Identify by its dark color and visible interlocking crystals of plagioclase feldspar and pyroxene. Commonly found in ophiolite complexes and eroded mountain ranges.
