igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6 on Mohs scale; Color: Dark grey to black, weathering to brownish-green; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal fracture); Specific gravity: 2.8-3.0.

Hardness: 6 on Mohs scale
Color: Dark grey to black, weathering to brownish-green
Luster: Dull to sub-vitreous

Identified May 28, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. It is the most common volcanic rock on Earth and makes up most of the ocean floor.

Uses & applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for floor tiles or monuments.

Geological facts

Basalt is also found on the Moon, Mars, and Venus. The 'Maria' on the lower parts of the Moon are actually vast basaltic plains. It can form unique geometric columns like those at the Giant's Causeway.

Field identification & locations

Identify by its dark color, heavy weight (density), and lack of visible large crystals. Commonly found in volcanic regions, oceanic islands (like Hawaii), and large igneous provinces.

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