igneous

Basalt

Basalt (Extrusive Mafic Igneous)

Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic), often crystalline but too small to see; Specific Gravity: 2.8-3.0

Hardness: 6
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 20, 2026More igneous →

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Physical properties

Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic), often crystalline but too small to see; Specific Gravity: 2.8-3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the surface of a terrestrial planet or moon. Basalt comprises more than 90% of all volcanic rock on Earth.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Can also be used for decorative stone and stone wool insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up the entirety of the ocean floor. It is also found on the Moon, Mars, and Venus.

Field identification & locations

Identified by its dark color, heavy weight (relative to size), and fine-grained texture. It often breaks with a conchoidal fracture and lack of visible 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