Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull/Matte; Structure: Aphanitic (fine-grained), sometimes vesicular; Cleavage: None/Conchoidal fracture; 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. It is an extrusive igneous rock found in volcanic regions worldwide.

Uses & Applications

Widely used in construction for aggregate, road base, railroad ballast, and concrete. It is also used as a raw material for stone wool insulation and occasionally as decorative stone or in high-end countertops.

Geological Facts

Basalt is the most common rock on Earth's surface, making up most of the ocean floor and large volcanic provinces. It is also extremely common on the Moon and Mars.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (relative to size), and very fine grain where individual crystals are too small to see with the naked eye. Often breaks with sharp, jagged edges.

Identified on: 5/1/2026

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