Basalt Pebble

Physical Properties

Hardness: 6.0; Color: Dark gray to black (appearing blueish-gray when wet); Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Presence of small vesicles (gas bubbles).

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

Used primarily in construction as aggregate for concrete and asphalt, road base, and railroad ballast. Exceptionally smooth pebbles are used in landscaping and massage therapy.

Geological Facts

Basalt is the most common volcanic rock on Earth and also makes up most of the ocean floors. It is also found on the Moon and Mars.

Field Identification & Locations

Identify by its dark, heavy, and fine-grained matrix. Look for small holes (vesicles) on the surface where gases escaped during cooling. Commonly found on beaches near volcanic regions.

Identified on: 4/26/2026

Mode: Standard