sedimentary

Chert (White Chert)

Silicon Dioxide (SiO2)

Hardness: 7 Mohs; Color: White to off-white; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 Mohs
Color: White to off-white
Luster: Dull to waxy

Identified May 30, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: White to off-white; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed as nodules or layers in limestone or chalk through the accumulation of siliceous remains (like sponge spicules or radiolarians) or chemical precipitation from hydrothermal fluids.

Uses & applications

Historically used for making stone tools (arrowheads). Modernly used as a road aggregate, in jewelry as 'flint', and as a fire-starting material.

Geological facts

Chert was one of the most important raw materials for early humans due to its ability to fracture into sharp edges. It is chemically identical to quartz but with a different micro structure.

Field identification & locations

Identify by its waxy appearance and conchoidal (shell-like) fracture patterns. It cannot be scratched by a steel pocket knife. Found globally in sedimentary rock outcrops.