igneous

Basalt

Basalt (Mafic Extrusive Igneous Rock)

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

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

Identified May 18, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull; Crystal structure: Aphanitic (fine-grained) to porphyritic; 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 basalt flows are from the Cenozoic era or volcanic hot spots.

Uses & applications

Extensively used in construction as aggregate for roads, railroad ballast, and concrete. Also used for high-quality paving stones and as a component in stonewool insulation.

Geological facts

Basalt is the most common rock on Earth's surface, making up most of the ocean floor. It is also found on the Moon, Mars, and Venus.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to volume), and very fine-grained texture that lacks visible individual crystals to the naked eye. Found worldwide 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