sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Tan, brown, or earthy yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Tan, brown, or earthy yellow
Luster: Waxy to dull

Identified June 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica in sedimentary environments, often through the accumulation of siliceous biological remains like radiolaria or through chemical replacement of limestone or chalk.

Uses & applications

Historically used for stone tools due to sharp edges; currently used as a road aggregate, in landscaping, and some varieties as semi-precious gemstones.

Geological facts

Chert is essentially the same mineral as flint, though flint is typically used to describe dark varieties. It can have extremely sharp edges when broken, which were once used to make arrowheads and knives.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and its shell-like (conchoidal) fracture pattern. It is common in limestone formations and as river pebbles.