River Stone (likely Quartzite or Chert)

Physical Properties

Hardness: 7 (Mohs scale); Color: Grayish-green with darker inclusions/veining; Luster: Waxy to dull (smooth due to water erosion); Crystal structure: Cryptocrystalline or granular; Cleavage: None (conchoidal fracture).

Formation & Geological History

Formed through the metamorphism of quartz sandstone (quartzite) or the precipitation of microcrystalline silica (chert). This specific specimen has been significantly rounded and smoothed by transport in high-energy water environments like rivers or beaches.

Uses & Applications

Common river stones are used for landscaping, decorative gravel, aquarium substrate, and occasionally as 'pocket stones' or for rock tumbling.

Geological Facts

Smooth river stones like this are often called 'clasts' in geology. Their rounded shape is a direct result of 'abrasion'—the process where rocks bang against each other in water, wearing down sharp edges over hundreds of years.

Field Identification & Locations

Identify in the field by its smooth, oval shape and extreme hardness (will scratch glass). Commonly found in riverbeds, glacial tills, and coastal areas. It is a staple specimen for beginners learning about erosion and the rock cycle.

Identified on: 4/15/2026

Mode: Standard