igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6.0 on Mohs scale; Color: Dark grey, black, or dark greenish-grey; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0. Note the conchoidal-to-uneven fracture visible in the image.

Hardness: 6
Color: Dark grey, black, or dark greenish-grey
Luster: Dull to sub-metallic

Identified April 7, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface of a terrestrial planet or a moon. Most basalt flows on Earth were formed during the Cenozoic era, though it has been produced throughout Earth's history.

Uses & applications

Extensively used in construction for aggregate, road base, concrete, and railroad ballast. It is also used as dimension stone for tiles and monuments and in the production of stone wool insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It also covers vast areas of the Moon, known as the lunar maria, and is the primary rock type on Mars and Venus.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture that lacks visible crystals to the naked eye. It is commonly found in volcanic regions, oceanic islands (like Hawaii), 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