Chert (Jasper/Chalcedony)

Physical Properties

Hardness: 6.5-7 on Mohs scale. Color: Tan, yellowish-brown, opaque. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Formation & Geological History

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous to Paleozoic in age.

Uses & Applications

Historically used for stone tools and arrowheads due to sharp edges when fractured. Currently used for gravel, road surfacing, decorative landscaping, and occasionally lapidary work.

Geological Facts

Chert and its varieties like flint and jasper were the primary materials for human technology for millions of years. This specimen shows significant river-rounding or water-wear, giving it a smooth, pebble-like texture.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its waxy appearance. Look for conchoidal (shell-like) fractures on broken edges. Common in riverbeds and limestone outcrops.

Identified on: 4/13/2026

Mode: Standard