igneous

Basalt

Aphanitic mafic volcanic rock (primarily plagioclase feldspar and pyroxene)

Hardness (Mohs scale): 6; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic (if minerals are visible); Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0.

Color: Dark grey to black, weathering to brown
Luster: Dull to sub-metallic (if minerals are visible)

Identified March 8, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava. Common in oceanic crust, mid-ocean ridges, and volcanic hotspot regions. Ages range from modern eruptions to billions of years old.

Uses & applications

Extensively used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as stone 'wool' for insulation and in high-end floor tiles or statues.

Geological facts

Basalt is the most common rock on Earth's surface and also covers vast areas of the Moon (the 'Maria') and Mars. It forms hexagonal columns (columnar jointing) when thick lava flows cool and contract slowly.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and lack of visible large crystals unless it is porphyritic. It is found globally in volcanic fields, notably in the Pacific Northwest USA and Iceland.

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