Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Cleavage: None (subconchoidal fracture).

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specimen appears water-worn into a pebble shape, likely in a river or coastal environment.

Uses & Applications

Used in construction as road base, railroad ballast, and concrete aggregate. High-quality dense basalt is also used for dimensional stone, sculptures, and stone massage sets.

Geological Facts

Basalt is the most common rock on Earth's surface and actually makes up most of the ocean floor. It is also found on the Moon and Mars.

Field Identification & Locations

Identify by its heavy weight (high density), dark color, and fine grain where individual crystals are too small to see with the naked eye. To verify, look for its associated magnetic properties if magnetite is present.

Identified on: 4/22/2026

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