sedimentary

Chert (Flint)

Microcrystalline quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, grey, and cream; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, beige, grey, and cream
Luster: Waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, grey, and cream; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms or via chemical precipitation from silica-rich fluids within limestone or chalk beds. It is often found in nodules or bedded layers in rock sequences ranging from Precambrian to Cenozoic ages.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges. Modern uses include road surfacing, decorative landscaping, and as a component in some ceramics.

Geological facts

Because it fractures conchoidally like glass, chert was one of the most important minerals for early humans to create arrowheads, scrapers, and knives. It is also used to create sparks when struck against steel.

Field identification & locations

Identify in the field by its waxy texture, extreme hardness (it will scratch glass), and the way it breaks into smooth, curved surfaces. Commonly found in areas with limestone or dolomite outcrops.