igneous

Basalt

Extrusive mafic igneous rock

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

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

Identified May 6, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: dark grey to black or greenish-grey; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained) to porphyritic; 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 common rock type in the Earth's crust.

Uses & applications

Used extensively in construction (crushed stone for road base and concrete aggregate), high-quality floor tiles, monument stone, and as a raw material for stone wool insulation.

Geological facts

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

Field identification & locations

Identify in the field by its dark color, fine grain, and high density. Commonly found at volcanic sites, tectonic divergent boundaries, and oceanic seafloors.

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