sedimentary

Chert (variations include Flint)

Chert (SiO2)

Hardness: 7 Mohs scale; Color: Grey, tan, brown, or dull green with waxy luster; Crystal Structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65.

Hardness: 7 Mohs scale
Color: Grey, tan, brown, or dull green with waxy luster

Identified May 11, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Grey, tan, brown, or dull green with waxy luster; Crystal Structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments; commonly found in limestone or chalk beds.

Uses & applications

Historically used for stone tools and starting fires; currently used as road aggregate, in glass manufacturing, and as a decorative stone.

Geological facts

Chert is so hard it can scratch steel; it was one of the most vital materials for early humans to create arrowheads and knives due to its sharp, glass-like edges when broken.

Field identification & locations

Identify by its smooth, waxy surface and shell-like (conchoidal) fracture pattern. Found globally in sedimentary basins, riverbeds, and as nodules in limestone cliffs.