igneous

Basalt

Extrusive mafic igneous rock

Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0

Hardness: 6 (Mohs)
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 6, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface of a planet or moon. Most basalt on Earth was formed during the Cenozoic Era, covering much of the ocean floor.

Uses & applications

Used in construction as crushed stone for road base and concrete aggregate, in the manufacture of rock wool (insulation), and as polished decorative stones or for massage therapy.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars, forming the lunar maria (dark plains).

Field identification & locations

Identify by its heavy weight (high density), dark color, and fine-grained texture that lacks visible crystals to the naked eye. Commonly found at volcanic sites and riverbeds in volcanic regions.

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