igneous

Basalt

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

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic (if metallic minerals present); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9-3.1

Hardness: 6 (Mohs scale)
Color: Dark grey to black, weathering to brown
Luster: Dull to sub-metallic (if metallic minerals present)

Identified April 7, 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. It is the most common rock type in the Earth's crust, forming most of the ocean floor.

Uses & applications

Extensively used in construction, especially as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as dimension stone for tiles and monuments.

Geological facts

Basalt is the most voluminous rock on the Earth's surface and also covers large areas of the Moon (the dark lunar maria), Mars, and Venus. It is the source of rich volcanic soils.

Field identification & locations

Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. In the field, it often forms cooling columns (hexagonal) if in large flows.

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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral