Basalt

Physical Properties

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic, 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 exposed at or very near the surface of a terrestrial planet or moon. Most basalt flows are from the Cenozoic era or younger.

Uses & Applications

Majorly used in construction for aggregate, road base, concrete, and railroad ballast. Also used as dimension stone and high-grade insulation (rock wool).

Geological Facts

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

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and very fine grains that aren't visible to the naked eye. Commonly found in coastal areas, volcanic islands, and oceanic ridges.

Identified on: 5/2/2026

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