sedimentary

Chert (Flint)

Cryptocrystalline Silica (SiO2)

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

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

Identified July 21, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed in marine or lacustrine environments through the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or via chemical precipitation from silica-rich fluids within sedimentary rock layers.

Uses & applications

Historically used for stone tools (knapping) and fire-starting; currently used as a road aggregate, in jewelry as cabochons, and as a decorative landscaping stone.

Geological facts

Chert has been used by humans for hundreds of thousands of years to create sharp edges for hunting and domestic tools. When struck against steel, it produces sparks used to ignite fire.

Field identification & locations

Identified by its extreme hardness (cannot be scratched by a steel blade), waxy feel, and characteristic shell-like (conchoidal) fracture patterns where it breaks. Commonly found in limestone or chalk beds.