Basalt

Physical Properties

Hardness: 6.0; Color: Dark grey to black, weathering to brown; 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.

Uses & Applications

Used in construction as crushed stone for road bases and railroad ballast, in concrete aggregate, and sometimes in stone carving or as floor tiles.

Geological Facts

Basalt is the most common rock type in the Earth's crust; most of the ocean floor is basalt. It is also found on the Moon, Mars, and Venus.

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and very fine grains that are hard to see without a lens. Often found in volcanic areas or coastal regions.

Identified on: 4/22/2026

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