Basalt

Physical Properties

Hardness: 6.0 on Mohs scale; Color: Black or dark gray; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0.

Formation & Geological History

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava (basaltic lava) at or very near the Earth's surface.

Uses & Applications

Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Fine-grained specimens are used for stone carving and as thermal insulation (rock wool).

Geological Facts

Basalt is the most common rock type in the Earth's crust and makes up the majority of the ocean floor. It is also found in large quantities on the Moon and Mars.

Field Identification & Locations

Identified by its dark color, high density, and fine-grained texture. Commonly found in volcanic regions, oceanic islands (like Hawaii), and large igneous provinces.

Identified on: 5/14/2026

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