igneous

Gabbro

Plutonic mafic rock

Hardness: 6-7 (Mohs scale), Color: Dark gray to black (mafic), Luster: Phaneritic (medium to coarse crystalline), Crystal structure: Equigranular, Cleavage: Usually distinct in the component pyroxene and plagioclase, Specific Gravity: 2.7-3.3

Identified April 7, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow crystallization of magnesium-rich and iron-rich magma inside the Earth's crust. It is often found in the lower part of the oceanic crust during various geological eras including the Precambrian to Cenozoic.

Uses & applications

Used in construction as 'black granite' for countertops, floor tiles, and gravestones. Also used as crushed stone for road base material and railroad ballast.

Geological facts

Gabbro is the intrusive equivalent of basalt. It is essentially the same chemical composition as basalt but cooled much slower, allowing larger crystals to grow visible to the naked eye.

Field identification & locations

Identify in the field by its dark color and visible, interlocking crystals of pyroxene and dark plagioclase feldspar. Commonly found in large igneous provinces and mid-ocean ridges.

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