Basalt

Physical Properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Earthy; 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. This specific specimen appears to be a water-worn river pebble or beach stone.

Uses & Applications

Commonly used as aggregate in construction, road base, concrete, and as decorative landscaping stones.

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 common on the Moon and Mars.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture with no visible crystals to the naked eye. Frequently found near volcanic sites, coastal areas, or riverbeds downstream from volcanic zones.

Identified on: 4/13/2026

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