igneous

Basalt

Extrusive mafic igneous rock

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic, Crystal structure: Aphanitic (fine-grained), Cleavage: None/Conchoidal fracture, Specific gravity: 2.8–3.0

Identified May 28, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic, Crystal structure: Aphanitic (fine-grained), Cleavage: None/Conchoidal fracture, 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 Earth's surface. Found in oceanic crust, volcanic islands, and flood basalt provinces.

Uses & applications

Used primarily in construction for road base, concrete aggregate, railroad ballast, and high-quality stone wool insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust and it also makes up most of the surface of the Moon, Mars, and Venus.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture lacking visible crystals. Common in areas of past volcanic activity.

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