igneous

Basalt

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained/microscopic); Cleavage: None; Specific Gravity: 2.8-3.0.

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified April 7, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained/microscopic); Cleavage: None; Specific Gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and volcanic regions.

Uses & applications

Used primarily in construction for crushed stone, road base, concrete aggregate, and railroad ballast. Some high-density basalt is used for insulation (rock wool).

Geological facts

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

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture. It often shows vesicular (bubbly) textures if gases were trapped during cooling. Found globally in volcanic fields.

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