igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6-7 (Mohs); Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained); Cleavage: none; Specific Gravity: 2.8–3.0

Hardness: 6-7 (Mohs)
Color: dark grey to black
Luster: dull to sub-metallic

Identified April 4, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs); Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained); Cleavage: none; Specific Gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. Most terrestrial basalt formed during the Cenozoic era, but it can be of any geological age.

Uses & applications

Extensively used in construction, especially as crushed stone for road base, concrete aggregate, and railroad ballast. It is also used in the manufacture 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 found on the Moon, Mars, and Venus.

Field identification & locations

Identify by its heavy weight (density), dark color, and lack of visible crystals to the naked eye. Often found in volcanic fields, plateaus, and ocean ridges.

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