igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to vitreous; Crystal structure: fine-grained (aphanitic) or glassy; Cleavage: none; Specific Gravity: 2.8–3.0

Hardness: 6 on Mohs scale
Color: dark grey to black
Luster: dull to vitreous

Identified February 21, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to vitreous; Crystal structure: fine-grained (aphanitic) or glassy; Cleavage: none; Specific Gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most common rock type in Earth's crust (oceanic crust).

Uses & applications

Widely used as an aggregate in construction projects, road base, concrete, and railroad ballast. Also used as dimension stone for tiles and counter tops.

Geological facts

Basalt is the most common rock type on Earth's surface and also makes up the vast majority of the lunar maria (the dark plains on the moon).

Field identification & locations

Identified by its heavy weight, dark color, and fine texture. Found in volcanic regions like the Pacific Northwest, Hawaii, and Iceland. Tools for collectors include a hand lens to see micro-crystals.

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