Igneous

Basalt

Mafic Igneous Rock (composed primarily of Pyroxene and Plagioclase Feldspar)

Hardness: 6 (Mohs scale); Color: Dark gray to black (often weathers to brown/green); Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained, invisible crystals); Specific gravity: 2.8 - 3.0.

Hardness: 6 (Mohs scale)
Color: Dark gray to black (often weathers to brown/green)
Luster: Dull to sub-metallic

Identified March 20, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of low-viscosity magnesium and iron-rich lava at or very near the surface. It is the most common rock in Earth's crust, making up most of the ocean floors. Geological age varies from modern volcanic flows to billions of years old.

Uses & applications

Extensively used as an aggregate in construction projects (road base, concrete, railroad ballast). Finely crushed basalt is used in agriculture for soil remineralization and as a raw material for stone wool insulation.

Geological facts

Basalt is also found on other terrestrial planets like Mars and Venus, and makes up the vast 'Maria' (dark plains) of the Moon. It is the extrusive equivalent of the intrusive rock Gabbro.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture. It often shows 'vesicles' (gas bubble holes) or a conchoidal fracture. Commonly found in volcanic regions, oceanic islands (like Hawaii), and mid-ocean ridges.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral