sedimentary

Chert (Chalcedony)

Microcrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, and creamy white; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Gray, tan, and creamy white
Luster: Waxy to dull

Identified June 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous remains of organisms or chemical precipitation of silica in sedimentary environments, often replacing carbonate rocks. Common throughout many geological eras from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and arrowheads due to conchoidal fracture. Modernly used for construction aggregate, jewelry (as jasper or agate), and as a collector's specimen.

Geological facts

Chert is so hard it can create sparks when struck against steel. Flint is a well-known dark variety of chert. It was one of the first materials used by early humans for technology.

Field identification & locations

Identify by its waxy luster, smoothness, and 'shell-like' conchoidal fractures. Commonly found in limestone or dolomite as nodules. Collectors should look for sharp edges and a texture that feels more like plastic or glass than sand.