sedimentary

Chert / Flint

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: typically grey, white, or tan in this specimen; Luster: dull to waxy; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: typically grey, white, or tan in this specimen
Luster: dull to waxy

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: typically grey, white, or tan in this specimen; Luster: dull to waxy; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of microcrystalline quartz in sedimentary rock layers, often through the replacement of calcium carbonate or by the accumulation of siliceous organisms like diatoms and radiolarians.

Uses & applications

Historically used for stone tools and starting fires; currently used as road aggregate, in glass making, and as decorative gravel.

Geological facts

Flint is a variety of chert. Due to its conchoidal fracture, it was the primary material for prehistoric arrowheads and knife blades. It produces sparks when struck against steel.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and curved, glass-like fracture surfaces. Frequently found in limestone or chalk deposits as nodules.