igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal Structure: Fine-grained (Aphanitic); Specific Gravity: 2.8-3.0; Cleavage: None.

Hardness: 6 (Mohs)
Color: Dark gray to black
Luster: Dull to sub-vitreous

Identified May 3, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal Structure: Fine-grained (Aphanitic); Specific Gravity: 2.8-3.0; Cleavage: None.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and volcanic regions.

Uses & applications

Used extensively in construction as road base, concrete aggregate, railroad ballast, and for high-quality paving stones. Also used in stone wool insulation.

Geological facts

Basalt is the most common rock on Earth's surface and covers most of the ocean floor. It is also found in abundance on the Moon and Mars.

Field identification & locations

Identify by its dark color, heavy weight compared to other small rocks, and very fine grains that are hard to see without magnification. Found in volcanic terrain.

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