Basalt

Physical Properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Sub-glassy; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Found on every continent and makes up most of the ocean floor.

Uses & Applications

Commonly used as crushed stone for road base, railroad ballast, and concrete aggregate. Used in high-performance insulation (rock wool) and as a building stone.

Geological Facts

Basalt is the most common rock in the Earth's crust. It is also found on the Moon, where it forms the dark areas known as 'Lunar Maria'.

Field Identification & Locations

Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. It often breaks with a slightly uneven or conchoidal fracture.

Identified on: 4/16/2026

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