sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Tan, beige, grey, or yellowish; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: Tan, beige, grey, or yellowish
Luster: Waxy to vitreous

Identified June 24, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Tan, beige, grey, or yellowish; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed in marine environments from the accumulation of silica-rich organisms (like diatoms or radiolarians) or chemical precipitation within limestone/chalk beds. Age varies from Precambrian to modern.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Today used in road construction, landscape gravel, and occasionally as semi-precious gemstones.

Geological facts

Chert has been used by humans for over 2 million years. When struck against steel, it produces sparks used to start fires, a characteristic that led to its use in flintlock firearms.

Field identification & locations

Identify by its conchoidal (shell-like) fracture pattern and its ability to scratch glass. It is commonly found as nodules within limestone or chalk layers in cliffs and stream beds.