igneous

Basalt

Hardness: 6.0; Color: Dark grey to black; Luster: Dull to vitreous; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0

Hardness: 6
Color: Dark grey to black
Luster: Dull to vitreous

Identified April 12, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull to vitreous; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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 Earth's surface. Common in oceanic crust and volcanic islands.

Uses & applications

Used primarily in construction for road base, concrete aggregate, asphalt pavement aggregate, railroad ballast, and high-quality stone tiles.

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, Mars, and Venus.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to its size), and lack of visible crystals. Commonly found in volcanic regions, near oceanic ridges, and river beds near volcanic plains.

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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