Chert (Yellow Jasper/River Rock)

Physical Properties

Hardness: 6.5-7 Mohs scale. Color: Opaque yellow, tan, and grey. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich fluids in sedimentary basins or the replacement of limestone. This specimen appears water-worn, likely tumbled in a river or coastal environment for thousands of years.

Uses & Applications

Historical use for stone tools (arrowheads), modern use in decorative landscaping, tumbled stones for jewelry, and as an industrial abrasive.

Geological Facts

Chert is so durable that it survives long-distance transport in rivers, which is why it is frequently found as rounded river pebbles. Variations colored by iron oxides are commonly called Jasper.

Field Identification & Locations

Identify by its 'waxy' feel and ability to scratch glass. Found globally in riverbeds and glacial tills. Common in areas with limestone bedrock.

Identified on: 4/19/2026

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