Basalt River Pebble

Physical Properties

Hardness: 6 on Mohs scale; Color: Black to dark grey; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8 to 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 has been rounded by fluvial or marine erosion.

Uses & Applications

Commonly used in construction as aggregate, for paving, and as decorative river stones in landscaping and architectural design. High-quality smooth stones are used in hot stone massage therapy.

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 found on the Moon and Mars.

Field Identification & Locations

Identified by its dark color, fine grain, and weight relative to size. Found globally in volcanic regions and riverbeds. For collectors, look for smoothness and uniform color.

Identified on: 5/20/2026

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