Chert (Jasper)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, grey, and tan banding; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed from the precipitation of silica-rich fluids within sedimentary rock layers or as microfossils (radiolarians/diatoms) on the ocean floor. Most specimens found today date from various eras, frequently Paleozoic to Cenozoic.

Uses & Applications

Historically used for making stone tools (flintknapping); currently used in jewelry (cabochons), as decorative landscaping stones, and for lapidary art.

Geological Facts

Chert is so hard that it was once the primary material for starting fires and crafting arrowheads before the advent of metallurgy. Red varieties are specifically called Jasper when they contain iron inclusions.

Field Identification & Locations

Identify in the field by its smooth, waxy feel and characteristic seashell-like (conchoidal) fractures. It is commonly found in riverbeds or within limestone and dolomite formations. It will scratch glass easily.

Identified on: 4/19/2026

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