igneous

Basalt

Extrusive mafic igneous rock

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

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

Identified May 23, 2026More igneous →

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Physical properties

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 moon. Basalt comprises more than 90% of all volcanic rock on Earth.

Uses & applications

Extensively used in construction, specifically as aggregate for roads, railroad ballast, and concrete. It is also used as dimension stone for tiles and floorings, and crushed for industrial high-temperature insulation.

Geological facts

Basalt is the most common rock type on Earth's crust and makes up most of the ocean floor. Large-scale eruptions of basalt can create 'Large Igneous Provinces' and it is the primary rock found on the Moon and Mars.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture which lacks visible crystals to the naked eye. Often found in volcanic regions, oceanic islands, and mid-ocean ridges.

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