sedimentary

Chert (varietal Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: yellowish-tan with a white cortex (weathered outer layer); Luster: waxy to dull; Breakage: conchoidal fracture (shell-like curves); Opaque to translucent.

Hardness: 7 on Mohs scale
Color: yellowish-tan with a white cortex (weathered outer layer)
Luster: waxy to dull

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: yellowish-tan with a white cortex (weathered outer layer); Luster: waxy to dull; Breakage: conchoidal fracture (shell-like curves); Opaque to translucent.

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) on the seafloor or by the replacement of carbonate rocks by silica-rich fluids. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used as a gemstone (Jasper), construction aggregate, and in landscaping.

Geological facts

This specimen shows a distinct white 'rind' or cortex, which is the result of chemical weathering of the silica. Chert was one of the most vital materials for prehistoric humans due to its sharp edges when broken.

Field identification & locations

Identify by its waxy texture, smooth conchoidal fractures, and extreme hardness (it will scratch glass). Common in sedimentary basins worldwide, particularly where limestone is present.