igneous

Basalt

Basalt (Mafic igneous rock)

Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic (can appear glossy when wet); Structure: fine-grained (aphanitic) or vesicular; Specific Gravity: 2.8–3.0.

Hardness: 6 on Mohs scale
Color: dark grey to black
Luster: dull to sub-metallic (can appear glossy when wet)

Identified April 10, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic (can appear glossy when wet); Structure: fine-grained (aphanitic) or vesicular; 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 type in the Earth's crust (oceanic crust).

Uses & applications

Extensively used in construction as aggregate, road base, concrete, and railroad ballast. Also used as dimension stone and for industrial purposes like rock wool insulation.

Geological facts

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

Field identification & locations

Identify in the field by its dark color, fine-grained texture, and high density. Often found in volcanic regions, at beaches near volcanic arches, or as river stones.

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