igneous

Basalt

Extrusive Igneous Basalt (contains Plagioclase Feldspar and Pyroxene)

Hardness: 6 (Mohs scale), Color: Dark grey to black (weathered surfaces may be brown), Luster: Dull or sub-metallic, Crystal structure: Aphanitic (fine-grained), Specific gravity: 2.8 - 3.0.

Identified April 12, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale), Color: Dark grey to black (weathered surfaces may be brown), Luster: Dull or sub-metallic, Crystal structure: Aphanitic (fine-grained), Specific gravity: 2.8 - 3.0.

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 in the Earth's crust.

Uses & applications

Extensively used in construction for aggregate, road base, concrete, and railroad ballast. It is also used as a thermal insulator in the form of rock wool and for stone carvings.

Geological facts

Basalt is the most common rock type on the surfaces of Mercury, Venus, the Moon, and Mars. It forms the entirety of the oceanic crust.

Field identification & locations

Identify by its dark color, heavy weight (density), and lack of visible crystals without a magnifying lens. Commonly found in lava flows, oceanic plates, and shield volcanoes like those in Hawaii or Iceland.

Other igneous specimens

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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