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

Identified May 31, 2026More igneous →

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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.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous