igneous

Basalt

Extrusive mafic igneous rock

Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0

Hardness: 6
Color: Dark grey to black
Luster: Dull/Matte

Identified May 9, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); 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. Often found in oceanic crust and volcanic regions.

Uses & applications

Used primarily in construction for aggregate, road base, and concrete; also used as a thermal insulator in stone wool form and occasionally for stonework and sculptures.

Geological facts

Basalt is the most common rock type on Earth's surface and also covers large areas of the Moon, Venus, and Mars (where it forms the giant volcano Olympus Mons).

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and lack of visible large crystals. Most common in volcanic fields, near faults, and along coastlines with volcanic history.

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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