Igneous

Basalt (Polished)

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6\u20137 Mohs; Color: Dark grey to black; Luster: Dull (naturally) to Sub-vitreous (when polished); Crystal structure: Fine-grained/Aphanitic; Specific gravity: 2.8\u20133.0

Hardness: 6\u20137 Mohs
Color: Dark grey to black
Luster: Dull (naturally) to Sub-vitreous (when polished)

Identified April 13, 2026More igneous →

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Physical properties

Hardness: 6\u20137 Mohs; Color: Dark grey to black; Luster: Dull (naturally) to Sub-vitreous (when polished); Crystal structure: Fine-grained/Aphanitic; Specific gravity: 2.8\u20133.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface of Earth. It is the most common rock in the Earth's crust, found in oceanic plates and large volcanic provinces.

Uses & applications

Used in construction (as aggregate or road base), decorative landscaping, 'hot stone' massage therapy, and occasionally for carved polished figurines or jewelry.

Geological facts

Basalt is also found on other planets, including Mars and Venus, and makes up the vast majority of the lunar maria (the dark plains on the moon).

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and lack of visible crystals to the naked eye. In the field, it often forms distinct hexagonal columns if part of a large flow.

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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral