igneous

Basalt with minor mineral crusting

Sideromelane / Extrusive Igneous Rock

Hardness: 6 (Mohs scale), Color: Dark grey to black with brown weathered exterior, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None

Identified May 26, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale), Color: Dark grey to black with brown weathered exterior, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. Common in volcanic regions and ocean floor crust.

Uses & applications

Primary use in construction (aggregate, asphalt, railroad ballast), industrial stone wool production, and occasionally used as a decorative landscape stone.

Geological facts

Basalt is the most common rock type on Earth's crust and even makes up much of the surface of the Moon, Mars, and Venus.

Field identification & locations

Identify in the field by its heavy weight (high density), dark color, and fine-grained texture. It often shows weathered brownish rinds when exposed to oxygen.

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