sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Reddish-brown to purple; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Reddish-brown to purple
Luster: Waxy to dull

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Reddish-brown to purple; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed by the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians) in marine environments. Often found in limestone or dolomite beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modernly used as road aggregate, architectural stone, and occasionally in jewelry as jasper.

Geological facts

Chert has been used by humans for hundreds of thousands of years. When it is red or brownish, it is often specifically referred to as jasper. It can produce sparks when struck against steel, similar to flint.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and its shell-like (conchoidal) breaking pattern. It feels smooth and waxy to the touch. Commonly found in riverbeds or as nodules in limestone outcrops.