igneous

Gabbro

Gabbro (Mg, Fe)2Si2O6 / CaAl2Si2O8

Hardness: 6-7 on Mohs scale; Color: Dark grey to black, sometimes with greenish tints; Luster: Phaneritic (coarse-grained), vitreous to dull; Crystal structure: Massive/Granular; Cleavage: Two directions at 90 degrees (pyroxene); Specific gravity: 2.7-3.3

Hardness: 6-7 on Mohs scale
Color: Dark grey to black, sometimes with greenish tints
Luster: Phaneritic (coarse-grained), vitreous to dull

Identified May 31, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of magnesium-rich and iron-rich magma deep beneath the Earth's surface (plutonic). It is the intrusive equivalent of basalt and is typically associated with oceanic crust and mid-ocean ridges.

Uses & applications

Used primarily as crushed stone for concrete aggregate and road base. Polished varieties are sold as 'Black Granite' for kitchen countertops, floor tiles, and cemetery markers.

Geological facts

Gabbro makes up a large portion of the deep oceanic crust. The name was coined by Christian Leopold von Buch in the late 1700s, named after a town in Tuscany, Italy.

Field identification & locations

Identify in the field by its dark color and visible, interlocking crystals of similar size. Often found in layered intrusions or ophiolite complexes. Look for the absence of quartz and the presence of dark plagioclase feldspar and pyroxene.

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