Igneous

Basalt

Mafic Volcanic Rock (composed of plagioclase, pyroxene, and olivine)

Hardness: 6 on Mohs scale; Color: charcoal gray to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8 - 3.0

Hardness: 6 on Mohs scale
Color: charcoal gray to black
Luster: dull to earthy

Identified March 22, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: charcoal gray to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8 - 3.0

Formation & geological history

Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron at or very near the Earth's surface (extrusive igneous process).

Uses & applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for paving or sculptures.

Geological facts

Basalt is the most common rock type in Earth's crust and makes up most of the ocean floors. It is also common on the Moon, Mars, and Venus.

Field identification & locations

Identify by its dark color, heavy weight (density), and lack of visible large crystals to the naked eye. Found worldwide in volcanic fields and mid-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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral