Basalt

Physical Properties

Hardness: 6-7 (Mohs); Color: Dark gray to black; Luster: Dull to sub-vitreous; 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 near the Earth's surface. Common in oceanic crust and volcanic regions.

Uses & Applications

Used extensively in construction for aggregate, road base, asphalt, and concrete. Also used for river rocks in landscaping and hot stone massage therapy.

Geological Facts

Basalt is the most common rock type in Earth's crust and makes up most of the ocean floors. It is also found on the Moon and Mars.

Field Identification & Locations

Identify by its heavy weight, dark color, and lack of visible crystals. Commonly found on beaches as smooth pebbles or near volcanic basalt columns.

Identified on: 5/7/2026

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