Basalt

Physical Properties

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

Formation & Geological History

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. Most basaltic formations are from the Cenozoic era, though it has formed throughout Earth's history.

Uses & Applications

Extensively used in construction, especially as crushed stone for road bases, concrete aggregate, and railroad ballast. It is also used in high-quality floor tiles and as 'basalt fiber' in industrial textiles.

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 common on other planetary bodies like the Moon, Mars, and Venus.

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and very fine-grained texture with no visible crystals to the naked eye. Commonly found in volcanic regions, oceanic crustal outcrops, and large plateau provinces like the Columbia River Basalt Group.

Identified on: 4/20/2026

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