igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6 Mohs; Color: dark gray to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; Specific gravity: 2.8-3.0.

Hardness: 6 Mohs
Color: dark gray to black
Luster: dull to earthy

Identified May 28, 2026More igneous →

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Physical properties

Hardness: 6 Mohs; Color: dark gray to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; Specific gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Found in oceanic crust, volcanic islands, and flood basalts.

Uses & applications

Used primarily in construction for aggregate, road base, railroad ballast, and ground-up for high-quality industrial stone wool insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust and also covers large areas of the lunar surface (the lunar Maria) and Mars.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture with no visible crystals to the naked eye. Commonly found in volcanic regions.

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