Basalt

Physical Properties

Hardness: 6.0 on Mohs scale; Color: dark grey to black upon fresh fracture, brownish-grey when weathered; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic), sometimes vesicular; Specific gravity: approx. 2.8–3.0.

Formation & Geological History

Forms 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. Most common rock type in the Earth's crust.

Uses & Applications

Commonly used in construction for aggregate in concrete and asphalt, as road base, and for railroad ballast. Occasionally used in stone carvings or as floor tiles.

Geological Facts

Basalt is the primary rock of the ocean floors and is the most common volcanic rock on Earth. It is also found on the Moon, Mars, and Venus.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It often lacks visible crystals to the naked eye. Look for hexagonal cooling columns in larger formations.

Identified on: 4/14/2026

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