sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Dark brown to black with a yellowish-tan weathered cortex; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Dark brown to black with a yellowish-tan weathered cortex
Luster: Waxy to vitreous

Identified June 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms or the chemical precipitation of silica in sedimentary basins. These specimens often occur as nodules within limestone or chalk beds, frequently dating from the Cretaceous to Mississippian periods.

Uses & applications

Historically used for stone tools (knapping) and making fire (striking steel). Modern uses include high-end road construction material, decorative landscaping, and occasionally as a gemstone in jewelry when it displays unique patterns.

Geological facts

Flint was one of the most important minerals for early human survival, used to create razor-sharp arrowheads and spears. The 'flintlock' mechanism on early firearms relied on this rock's ability to produce sparks when struck.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture pattern and its ability to scratch glass. Look for nodules in chalk or limestone outcrops. Collectors should look for sharp edges and distinct color zoning.