Basalt

Physical Properties

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Sub-metallic (when fresh), 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 exposed at or very near the surface of a terrestrial planet or a moon. This specimen appears water-worn or weathered.

Uses & Applications

Used in construction as road base, railroad ballast, and aggregate in concrete. High-quality specimens are used in architectural stone and sculpture.

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 extremely common on the Moon and Mars.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows small holes called vesicles if gases were trapped during cooling.

Identified on: 4/25/2026

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