igneous

Basalt

Extrusive Mafic Igneous Rock (composed primarily of plagioclase, pyroxene, and olivine)

Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0.

Hardness: 6 on the Mohs scale
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified March 11, 2026More igneous →

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Physical properties

Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; 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 Earth's surface. It is the most common volcanic rock and found across all geological ages, especially in oceanic crust and large volcanic provinces.

Uses & applications

Extensively used in construction as aggregate for roads, railroad ballast, and concrete; used in industrial manufacturing for rock wool insulation; occasionally used for decorative stonework and massage stones.

Geological facts

Basalt comprises more than 90% of all volcanic rock on Earth. It is also found on the Moon, Mars, and Venus, with the lunar 'maria' or dark plains being comprised of ancient basaltic lava flows.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and lack of visible large crystal grains. It often exhibits columnar jointing in large formations. Found globally in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.

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