sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, brown, or reddish-brown with waxy luster; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, brown, or reddish-brown with waxy luster

Identified March 17, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, brown, or reddish-brown with waxy luster; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation from groundwater within limestone or chalk beds. Commonly associated with sedimentary rock layers of various geological ages.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road construction, landscape gravel, and occasionally for modern flint-knapping enthusiasts.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges; it is also capable of producing sparks when struck against steel.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found as nodules or layers within sedimentary rocks like limestone across the globe.