Basalt

Physical Properties

Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the surface of a planet or moon. Most basalt on Earth was formed within the last 200 million years.

Uses & Applications

Used extensively in construction as crushed stone for road base, railroad ballast, and concrete aggregate; also used for stone carvings and floor tiles.

Geological Facts

Basalt is the most common rock type in the Earth's crust and also makes up most of the ocean floor. Large areas of the Moon and Mars are also covered in basaltic lava plains.

Field Identification & Locations

Identify by its dark color, heavy weight compared to common stones, and fine-grained texture. Commonly found in volcanic regions, oceanic crust, and plate tectonic boundaries.

Identified on: 4/15/2026

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