River Rock

Hardness: 6-7 (Mohs), Color: Brown, tan, and grey with green algal coating, Luster: Dull to earthy when wet, Crystal structure: Microcrystalline to granular, Cleavage: None, Specific Gravity: 2.5-2.7

Formed through the erosion and transport of parent rock materials in a high-energy aquatic environment. Over thousands of years, water flow rounds the sharp edges of the stone via abrasion and hydraulic action. These are typically found in Holocene to Pleistocene riverbeds.

Primarily used in landscaping, aquarium decoration (as seen here), drainage systems, and as an aggregate in construction and concrete projects.

These rocks have been smoothed by thousands of years of tumbling in river currents. When submerged in slow-moving or stagnant water like a pond, they often develop a patina of green chlorophyta (green algae).

Identify by the distinctive rounded, smooth surface (sub-rounded to well-rounded) which indicates transport by water. Common in river valleys and glacial deposits globally.