Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) or vesicular; 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

Extensively used in construction for aggregate, road base, railroad ballast, and floor tiles. Finely ground basalt is used as a soil amendment.

Geological Facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. It also covers large areas of the Moon and Mars.

Field Identification & Locations

Identify by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.

Identified on: 5/1/2026

Mode: Standard