igneous

Gabbro

Phaneritic Mafic Igneous Rock

Hardness: 6-7 (Mohs scale); Color: Dark gray, black, or dark green with visible light-colored crystals; Luster: Vitreous to dull; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Distinct in pyroxene/plagioclase components; Specific Gravity: 2.7-3.3

Hardness: 6-7 (Mohs scale)
Luster: Vitreous to dull

Identified March 1, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow cooling of magnesium-rich and iron-rich magma deep beneath the Earth's surface (intrusive). It is chemically equivalent to basalt but cools at depth rather than on the surface. Commonly found in oceanic crust and large plutonic bodies.

Uses & applications

Used extensively in the construction industry as 'black granite' for countertops, floor tiles, and facing stone. Also used as crushed stone (aggregate) for road base, railroad ballast, and concrete.

Geological facts

Gabbro makes up a large portion of the Earth's lower oceanic crust. When it contains significant amounts of chromium, nickel, or platinum, it can be a valuable ore body. It is often confused with diorite, but gabbro contains more dark mafic minerals.

Field identification & locations

Identify in the field by its dark color and coarse, interlocking crystal texture where individual grains are visible to the naked eye. Look for the presence of dark olivine or pyroxene paired with grayish plagioclase. Found in mountainous or volcanic regions world-wide.

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