Chert / Jasper

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through chemical precipitation from silica-rich fluids in sedimentary basins.

Uses & Applications

Historically used for stone tools (arrowheads) due to its sharp edges; currently used in jewelry (as jasper), lapidary arts, and as an industrial abrasive.

Geological Facts

Chert was one of the most important materials for early humans because its conchoidal fracture allows it to be worked into sharp blades and tools. Flint is a variety of chert.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by a steel nail), waxy luster, and smooth, curved (conchoidal) breakage surfaces. Commonly found in limestone or chalk beds.

Identified on: 4/19/2026

Mode: Standard