Chert (Jasper variety)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and creamy opaque bands; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.91

Formation & Geological History

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids in sedimentary basins. This specimen shows iron oxide staining giving it the jasper-like color.

Uses & Applications

Historically used for stone tools (arrowheads/scrapers) due to conchoidal fracture. Currently used for lapidary work, jewelry cabochons, and as decorative landscape stone.

Geological Facts

Chert was one of the first materials used by early humans for tool-making. Jasper specifically is a name given to opaque chert that is pigmented by mineral impurities, usually iron.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife), its smooth waxy feel, and its shell-like (conchoidal) breaking pattern. Found globally in limestone and dolomite formations.

Identified on: 5/1/2026

Mode: Standard