igneous

Basalt

Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained) to porphyritic; Specific gravity: approx. 2.8–3.0

Hardness: 6 on Mohs scale
Color: dark grey to black
Luster: dull to sub-metallic

Identified May 12, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained) to porphyritic; Specific gravity: approx. 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 are Cenozoic in age, though they occur across all geological eras.

Uses & applications

Used primarily in construction for aggregate, road base, railroad ballast, and high-quality concrete. Can be used in stone sculpture and the manufacturing of stone wool insulation.

Geological facts

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

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. It often shows vesicules (small holes) or olivine crystals. Found globally 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