igneous

Basalt

Mafic extrusive volcanic rock (composed primarily of Plagioclase feldspar and Pyroxene)

Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or dark greenish-grey; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (irregular/conchoidal fracture); Specific Gravity: 2.8 - 3.0

Hardness: 5-6 (Mohs scale)
Color: Dark grey, black, or dark greenish-grey
Luster: Dull to sub-metallic

Identified February 19, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. Most basalt found on Earth is from the Cenozoic era or younger, though it exists across all geological ages.

Uses & applications

Extensively used in construction as aggregate for roads, railroad ballast, and concrete. It is also used as dimension stone for tiles and monuments, high-temperature insulation (stone wool), and occasionally used in jewelry when polished as 'Lava Stone'.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. It is also the primary rock found on the Moon and Mars. When cooling slowly in thick layers, it can form spectacular 'columnar jointing' like at the Giant's Causeway.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size due to iron content), and lack of visible crystals to the naked eye. It is found globally, particularly near volcanic ridges, oceanic islands (like Hawaii), and continental flood basalts.

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