Basalt (River Stone)

Physical Properties

Hardness: 6 (Mohs scale); Color: Dark grey to charcoal black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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 has been further shaped through fluvial or coastal erosion, creating a smooth, rounded 'cobble' or 'river stone' appearance.

Uses & Applications

Used extensively in construction as road base, concrete aggregate, and railroad ballast. Decorative uses include landscaping, massage stones, and aquarium decor.

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 heavy weight (relative to size), dark color, and lack of visible crystals. Commonly found in volcanic regions, riverbeds, and along shorelines. For collectors, look for smoothness and symmetry.

Identified on: 4/23/2026

Mode: Standard