igneous

Basalt

Mafic Igneous Basalt

Hardness: 6 on Mohs scale; Color: Dark grey to black, sometimes weathering to brown; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic), sometimes vesicular; Cleavage: None (conchoidal fracture).

Hardness: 6 on Mohs scale
Color: Dark grey to black, sometimes weathering to brown
Luster: Dull to sub-metallic

Identified April 6, 2026More igneous →

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Physical properties

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

Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Also used as dimension stone for pavement and monuments.

Geological facts

Basalt is the most common rock type on the Earth's surface and also covers large areas of the Moon, Mars, and Venus, known as 'maria' on the Moon.

Field identification & locations

Identify by its dark color, heavy weight (high density), and fine grain that is usually too small to see with the naked eye. Found in volcanic terrain or riverbeds near volcanic sources.

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