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) to porphyritic; Specific gravity: 2.8-3.0; Cleavage: None.

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

Identified April 9, 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) to porphyritic; Specific gravity: 2.8-3.0; Cleavage: None.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava (mafic lava) at or very near the Earth's surface. It can be found across all geological ages, notably in oceanic crust and large flood basalt provinces.

Uses & applications

Extensively used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as dimension stone and in the manufacturing of rock 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, Mars, and Venus.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and very fine-grained texture where individual crystals are not visible to the naked eye. Found in volcanic regions and oceanic islands like Hawaii or Iceland.

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