sedimentary

Chert (specifically Gray Chert)

Chert (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, and brownish-yellow; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, and brownish-yellow
Luster: Waxy to dull

Identified April 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or through chemical precipitation in marine or groundwater environments. Can vary in age from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used for decorative gravel, landscaping, and as a component in construction aggregate.

Geological facts

Chert is chemically identical to quartz but has a much finer crystal structure. When it occurs in chalk or marl, it is specifically referred to as flint.

Field identification & locations

Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is commonly found in stream beds or as nodules within limestone layers.