sedimentary

Chert (specifically Flint)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7.0 on Mohs scale; Color: typically dark grey, black, or brown; Luster: waxy to dull; Structure: microcrystalline (no visible grains); Cleavage: none, exhibits distinct conchoidal (shell-like) fracture; Specific Gravity: 2.65.

Hardness: 7
Color: typically dark grey, black, or brown
Luster: waxy to dull

Identified March 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine or freshwater environments via the replacement of carbonate minerals by silica-rich fluids. It often occurs as nodules or layers within limestone and chalk beds. Common in deposits from the Paleozoic and Mesozoic eras.

Uses & applications

Historically used for stone tools (arrowheads/knives) due to its sharp edges and as a fire-starting striking material. Modern uses include decorative gravel, road construction, and occasionally in gemstone tumbling.

Geological facts

Flint was a vital survival tool for prehistoric humans. When struck against steel (or iron pyrite), it creates hot sparks used for fire-making and was the mechanism for flintlock firearms.

Field identification & locations

Identify by its 'glassy' smooth texture when broken and razor-sharp edges. It is found globally, notably in the chalk cliffs of the UK and across North America. To identify, check for its ability to scratch glass and its curved, shell-like fracture pattern.