sedimentary

Chert / Flint

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: typically gray, brown, or buff; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: typically gray, brown, or buff
Luster: waxy to dull

Identified March 23, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically gray, brown, or buff; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of siliceous remains of organisms like diatoms and radiolarians, or through chemical precipitation in marine or groundwater environments. Can occur as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads, knives); currently used in road construction, as a flint-striker for fire starting, and occasionally for lapidary work.

Geological facts

Due to its conchoidal fracture, it breaks into razor-sharp edges, making it the primary material for the Stone Age technology. It is often referred to as 'flint' when found in chalk or marly limestone.

Field identification & locations

Identify in the field by its smooth, waxy surface and its tendency to break into curved, glass-like shards. Found globally, especially in regions with extensive limestone deposits like the UK, France, and the American Midwest.