Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); 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. Most basalt on Earth is less than 200 million years old.

Uses & Applications

Used extensively in construction for aggregate, road base, railroad ballast, and high-quality concrete. It is also used as a dimension stone for flooring and monuments.

Geological Facts

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

Field Identification & Locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture that lacks visible crystals to the naked eye. Found worldwide in volcanic regions and ocean basins.

Identified on: 5/18/2026

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