Basalt

Physical Properties

Hardness: 6.0 on Mohs scale. Color: Dark grey to black. Luster: Dull or sub-metallic. Crystal structure: Aphanitic (fine-grained), often containing small vesicles or phenocrysts. 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 common rock type in Earth's crust (oceanic crust).

Uses & Applications

Extensively used in construction, especially as crushed stone for road base, concrete aggregate, and railroad ballast. Can also be polished for floor tiles and monuments.

Geological Facts

Basalt is the most common rock on Earth and also makes up much of the surface of the Moon and Mars. On Earth, it forms the entire floor of the ocean basins.

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. Commonly found in volcanic regions and coastal areas where oceanic crust is exposed.

Identified on: 4/17/2026

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