sedimentary

Chert (Common Chert)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, brown, white, and gray; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Tan, brown, white, and gray
Luster: Dull to waxy

Identified February 21, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, brown, white, and gray; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed primarily through the precipitation of silica in marine environments or by the replacement of carbonate rocks by silica-rich fluids. It is found in geological strata ranging from Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Modern uses include road base construction material, gravel, and occasionally as a base for lapidary work.

Geological facts

Chert has been used by humans for over a million years because its conchoidal fracture creates sharp edges. 'Flint' is a variety of chert, typically found in chalk or marly limestone.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), waxy feel on fresh surfaces, and smooth, shell-like (conchoidal) fractures. It is commonly found as nodules in limestone or as bedded deposits.