igneous

Basalt

Extrusive Igneous Rock (Mafic)

Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), often contains micro-crystals of plagioclase/pyroxene. Specific gravity: 2.8-3.0.

Hardness: 5-6 Mohs
Color: Dark gray to black
Luster: Dull to sub-metallic

Identified May 25, 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. Most basalt flows are from the Cenozoic era.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Can be used for stone carvings or as a component in rock wool insulation.

Geological facts

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

Field identification & locations

Identified in the field by its dark color, heavy weight (density), and fine-grained texture. Commonly found in oceanic crust, volcanic islands, and flood basalt provinces.

Other igneous specimens

See all

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