igneous

Basalt

Mafic Volcanic Rock (composed mainly of Plagioclase, Pyroxene, and Olivine)

Hardness: 6 (Mohs scale); Color: Dark gray to black (mafic); Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic) or porphyritic; Cleavage: None (conchoidal fracture common); Specific Gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark gray to black (mafic)
Luster: Dull to sub-metallic

Identified March 15, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the surface of a terrestrial planet. It covers most of the Earth's ocean floor and is commonly associated with shield volcanoes and oceanic hotspots.

Uses & applications

Extensively used in construction as aggregate for roads and concrete, railway ballast, and in the production of stone wool insulation. It is occasionally used in landscaping and as a base stone for masonry.

Geological facts

Basalt is the most common volcanic rock in the solar system, making up the vast majority of 'Mars' crust and the 'Maria' (dark plains) on the moon. It can form spectacular hexagonal columns during cooling, such as at the Giant's Causeway.

Field identification & locations

Identify by its dark, heavy, and fine-grained texture. It often features small vesicles (gas bubbles) or larger crystals (phenocrysts) embedded in a dark matrix. Common in the Pacific Northwest (Columbia River Basalt Group) and volcanic islands like Hawaii.

Other igneous specimens

See all

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