sedimentary

Chert (Flint variety)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Brown, grey, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Brown, grey, tan
Luster: Waxy to dull

Identified May 9, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, grey, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed as nodules in sedimentary rocks like limestone or chalk when silica replaces carbonate material or precipitates from fluids. This process often occurs over millions of years.

Uses & applications

Historically used for stone tools and starting fires; currently used in jewelry (tumbled stones), road surfacing, and as a refractory material.

Geological facts

Because of its conchoidal fracture, it can be chipped to a razor-sharp edge, which led prehistoric humans to use it for arrowheads and knives.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its waxy texture, and its smooth, curved (conchoidal) broken edges. Commonly found in river beds and limestone outcrops.