Basalt

Physical Properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull or sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.

Formation & Geological History

Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the Earth's surface. It can be found in volcanic regions and oceanic crust.

Uses & Applications

Extensively used in construction, specifically as road base, concrete aggregate, and railroad ballast. Well-formed columns may be used for architectural features.

Geological Facts

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

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture lacking visible crystals. Use a magnifying glass to check for tiny holes (vesicles).

Identified on: 4/20/2026

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