sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, grey, and black banding; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, grey, and black banding
Luster: Waxy to vitreous

Identified May 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, grey, and black banding; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the replacement of limestone/carbonate material by silica-rich fluids or the accumulation of siliceous organisms on the sea floor during the Phanerozoic Eon. This specimen shows water-worn smoothing suggesting secondary transport in a river or coastal environment.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) and fire-starting. Currently used in road construction as aggregate, lapidary arts, and as an industrial abrasive.

Geological facts

Chert is so durable that it often survives as 'river pebbles' long after the surrounding limestone host rock has eroded away. The dark variety is colloquially known as Flint and was essential to the Stone Age.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel nail) and characteristic curved 'conchoidal' fractures. Often found in gravel beds or embedded in limestone cliffs. Collectors look for unique banding or patterns.