igneous

Basalt

Mafic Volcanic Rock

Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or porphyritic; Cleavage: None; Specific Gravity: 2.8 - 3.0

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

Identified May 4, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or porphyritic; 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 surface of a terrestrial planet or a moon. It occurs throughout geological time, from the Archean eon to modern volcanic eruptions.

Uses & applications

Used primarily in construction (crushed stone for road bases and concrete aggregate), high-tensile fiber for insulation, and occasionally as structural stone or in landscaping.

Geological facts

Basalt is the most common volcanic rock on Earth and also makes up most of the surface of the Moon and Mars. On Earth, it forms the entirety of the oceanic crust.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows small white speckles of plagioclase or green crystals of olivine. Found worldwide in volcanic regions like Hawaii, the Pacific Northwest, and 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