sedimentary

Chert / Flint

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidally fractures); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified May 28, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidally fractures); Specific gravity: 2.65

Formation & geological history

Formed from the precipitation of silica-rich fluids in sedimentary environments, often replacing calcium carbonate or accumulating from the remains of silica-shelled organisms like diatoms and radiolarians.

Uses & applications

Historically used for stone tools and starting fires; currently used as a raw material for road construction, grit, and occasionally as architectural stone or semi-precious decorative stone.

Geological facts

Flint is a specialized type of chert often associated with chalk or marly limestone. It was the primary material for human tools (arrowheads, knives) for thousands of years because of its sharp edges when broken.

Field identification & locations

Identify by its 'flinty' or waxy appearance and shell-like (conchoidal) fracture edges. It is extremely hard and will scratch glass easily. Commonly found in limestone beds or as nodules on beaches.