igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull (aphanitic texture); Crystal structure: Fine-grained/microcrystalline; Cleavage: None; Specific gravity: 2.8 - 3.0

Hardness: 6 (Mohs scale)
Color: Dark gray to black
Luster: Dull (aphanitic texture)

Identified March 25, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull (aphanitic texture); Crystal structure: Fine-grained/microcrystalline; 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. It comprises more than 90% of all volcanic rock on Earth and characterizes oceanic crust.

Uses & applications

Extensively used in construction as aggregate (crushed stone) for road base, concrete, and railroad ballast. Also used as dimension stone for tiles and monuments, or for industrial 'stone wool' insulation.

Geological facts

Basalt is the most common rock in the solar system, making up the vast majority of the lunar maria on the Moon and the surface of Mars and Venus.

Field identification & locations

Identify in the field by its high density, dark color, and lack of visible large crystals. It is ubiquitous in volcanic regions like Iceland, Hawaii, and the Pacific Northwest. Collectors look for vesicles (air bubbles) containing zeolites or olivine crystals.

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