Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Fine-grained/Aphanitic; 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.

Uses & Applications

Used extensively in construction as road base, railroad ballast, and concrete aggregate. Sometimes used in dimension stone for flooring and monuments.

Geological Facts

Basalt is the most common volcanic rock on Earth and also makes up most of the oceanic crust and much of the surfaces of the Moon, Mars, and Venus.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (density), and lack of visible individual crystals without a lens. Found globally in volcanic provinces.

Identified on: 5/15/2026

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