sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5–7 (Mohs scale); Color: Brown, reddish-brown, tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.9

Hardness: 6
Color: Brown, reddish-brown, tan
Luster: Waxy to dull

Identified April 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) on the ocean floor or by the replacement of carbonate rocks by silica-rich fluids. This specimen appears to be an iron-rich variety often called Jasper.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp conchoidal fracture. Today used in jewelry (cabochons), as an ornamental stone, and in lapidary arts.

Geological facts

Chert is one of the most durable rocks on the planet. Because of its extreme hardness and ability to hold a sharp edge, it was the 'high-tech' material of the Stone Age, used by humans for millions of years before the discovery of metals.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass easily. It will not react with acid. Commonly found in stream beds or as nodules within limestone layers.