sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

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

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

Identified July 14, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed as nodules or beds in sedimentary rocks through the accumulation of siliceous remains of organisms (like diatoms) or by chemical precipitation of silica-rich groundwater. Often found in limestone or chalk deposits.

Uses & applications

Historically used for stone tools and starting fires (flint). Currently used in road construction, as a gemstone (jasper/agate varieties), and in chemical manufacturing.

Geological facts

Chert was one of the most important materials for early humans due to its ability to break into extremely sharp edges. It is chemically identical to quartz but has a different internal structure.

Field identification & locations

Identify by its waxy appearance and shell-like (conchoidal) fracture pattern. Look for it in creek beds or eroding out of limestone cliffs. It is often harder than a steel knife blade.