sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with waxy luster; Crystal Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Gray, tan, or brown with waxy luster

Identified June 10, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with waxy luster; Crystal Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or sponges) on the seafloor or by the replacement of calcium carbonate in limestone by silica-rich groundwater. Often found in nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used in construction as road aggregate, in glassmaking depending on purity, and for sparking 'flint' in survival gear.

Geological facts

Chert was one of the most important commodities in human prehistory; its ability to break into sharp edges made it the primary material for arrowheads and scrapers for millennia.

Field identification & locations

Identify in the field by its waxy appearance, smooth conchoidal (shell-like) fracture surfaces, and high hardness (it will scratch glass). Commonly found in stream beds or weathered out of limestone cliffs.