Basalt Pebble

Physical Properties

Hardness: 5-6 (Mohs scale); Color: Dark grey to charcoal; Luster: Dull/Matte (weathered); 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 specimen appears water-worn, likely tumbled in a river or coastal environment over thousands of years.

Uses & Applications

Basalt is used extensively in construction (aggregate, asphalt, railroad ballast) and sometimes for stone massage or aquarium decor. Smooth pebbles are popular in landscaping and decorative crafts.

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, Mars, and Venus.

Field Identification & Locations

Identify by its dark color, fine-grained texture, and significant weight relative to its size (high density). It will not react with acid like limestone and is typically found near volcanic regions or transported to coastlines.

Identified on: 4/23/2026

Mode: Standard