Chert (Chalcedony/Jasper)

Physical Properties

Hardness: 6.5-7 (Mohs scale), Color: tan, yellow, reddish-brown, Luster: waxy to vitreous, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Common in marine limestone sequences; age varies from Precambrian to Cenozoic.

Uses & Applications

Historically used for stone tools (flintknapping); currently used in landscaping, as semi-precious gemstones (jaspers), and as an abrasive in some industrial processes.

Geological Facts

This specimen appears to be a water-worn river pebble. Chert is so durable that it often survives long-distance transport in rivers and streams long after other rocks have eroded away.

Field Identification & Locations

Identified by its extreme hardness (cannot be scratched by a steel knife) and waxy, smooth texture. Look for smooth, rounded pebbles with translucent edges in gravel beds or stream deposits.

Identified on: 4/29/2026

Mode: Standard