igneous

Basalt (with possible fine-grained mineralization)

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brownish tones; Luster: Dull to sub-metallic on fresh surfaces; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark gray to black, often weathering to brownish tones
Luster: Dull to sub-metallic on fresh surfaces

Identified May 28, 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 a moon. Most common rock type in Earth's crust.

Uses & applications

Primarily used in construction for aggregate, road base, railroad ballast, and ground-up for asphalt and concrete. Occasionally used as dimension stone or for medicinal heat therapy stones.

Geological facts

Basalt is the most common rock on the Earth's surface and makes up most of the ocean floor. It is also found on the Moon and Mars.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and very fine-grained texture that lacks visible crystals to the naked eye. Found worldwide in volcanic provinces.

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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

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