Basalt

Physical Properties

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Earthy to sub-metallic, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8-3.0

Formation & Geological History

Forms 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

Primarily used in construction as aggregate, road base, concrete, and railroad ballast. Also used in stone carvings and as a high-strength basalt fiber.

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

Look for a heavy, dark-colored, fine-grained rock with small visible crystals. Commonly found in volcanic regions, oceanic crust, and plateaus created by flood basalts.

Identified on: 5/1/2026

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