igneous

Gabbro

Gabbro (Mafic Plutonic Rock)

Hardness: 6-7 on Mohs scale; Color: Dark grey, black, or dark green; Luster: Phaneritic (visible crystals), vitreous to dull; Crystal structure: Coarse-grained granular; Cleavage: Good in two directions (due to pyroxene); Specific gravity: 2.7 to 3.3

Hardness: 6-7 on Mohs scale
Color: Dark grey, black, or dark green
Luster: Phaneritic (visible crystals), vitreous to dull

Identified May 21, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow crystallization of magnesium-rich and iron-rich magma deep beneath the Earth's surface (plutonic). It is the intrusive equivalent to basalt and is often found in the lower oceanic crust.

Uses & applications

Used in the construction industry as 'black granite' for countertops, floor tiles, and facing stone; also crushed into aggregate for road base and railroad ballast.

Geological facts

Gabbro makes up a large portion of the deep oceanic crust. The name was given by the Italian geologist Christian Leopold von Buch after a town in the Tuscany region of Italy.

Field identification & locations

Identify by its dark color and coarse-grained texture where light-colored minerals (plagioclase) and dark minerals (pyroxene/olivine) are roughly equal in size. Commonly found in large igneous intrusions or ophiolite complexes.

Other igneous specimens

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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