igneous

Gabbro

Hardness: 6-7 on the Mohs scale; Color: Dark green, gray, to black; Luster: Phaneritic (crystalline) and somewhat dull to sub-metallic; Crystal Structure: Coarse-grained; Cleavage: Two directions at nearly 90 degrees (pyroxene); Specific Gravity: 2.7-3.3

Hardness: 6-7 on the Mohs scale
Color: Dark green, gray, to black
Luster: Phaneritic (crystalline) and somewhat dull to sub-metallic

Identified May 25, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed from the slow cooling of magnesium-rich and iron-rich magma deep beneath the Earth's surface (intrusive). They are often associated with mid-ocean ridges or ancient mountain-building events.

Uses & applications

Used as crushed stone for road construction, railroad ballast, and concrete aggregate. High-quality slabs are polished and sold as 'Black Granite' for kitchen countertops and floor tiles.

Geological facts

Gabbro is the intrusive equivalent of basalt; both have the same chemical composition but different crystal sizes. It makes up a significant portion of the deep oceanic crust.

Field identification & locations

Identify in the field by its dark color and coarse, visible interlocking crystals of plagioclase feldspar and pyroxene. It lacks the quartz typically found in granite. Commonly found in large plutons or ophiolite complexes.

Other igneous specimens

See all

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