Basalt

Physical Properties

Hardness: 5-6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Found in oceanic crust and volcanic regions.

Uses & Applications

Used in construction as crushed stone for road base, concrete aggregate, railroad ballast, and for high-temperature insulation in stone wool fibers.

Geological Facts

Basalt is the most common rock type in Earth's crust and also makes up most of the surface of the Moon and Mars.

Field Identification & Locations

Identify by its dark color, heavy weight (density), and fine-grained texture with no visible crystals to the naked eye. Found worldwide in volcanic fields.

Identified on: 5/20/2026

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