igneous

Basalt

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 7, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); 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. Often found in oceanic crust and huge volcanic plateaus.

Uses & applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for paving and flooring.

Geological facts

Basalt is the most common rock type in the Earth's crust and also covers large areas of the Moon, Mars, and Venus. The Giant's Causeway in Northern Ireland is a famous example of columnar basalt.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture that lacks visible crystals to the naked eye. Commonly found in volcanic regions and ocean floor samples.

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