sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

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

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

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by the chemical precipitation of silica in groundwater. Often found as nodules within limestone or as bedded deposits. Can range from Precambrian to Holocene in age.

Uses & applications

Historically used for making stone tools (arrowheads). Modernly used in jewelry (cabochons), as an abrasive, and in landscaping or construction aggregate.

Geological facts

Jasper is a variety of chert that is opaque due to high mineral impurities, usually iron oxides which give it the reddish-brown color. It has been used by humans for over 400,000 years for sharp-edged tools.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in riverbeds, glacial tills, and sedimentary outcrops worldwide. Collectors look for unique banding or 'orbicular' patterns.