sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Grey, white, tan, or greenish; Luster: Dull to waxy; Structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Grey, white, tan, or greenish
Luster: Dull to waxy

Identified June 10, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Grey, white, tan, or greenish; Luster: Dull to waxy; Structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the replacement of carbonate minerals in limestone or chalk beds. Often found as nodules in sedimentary layers.

Uses & applications

Historically used for stone tools (arrowheads). Today used as a component in aggregate for construction, occasionally in jewelry (as jasper/agate variants), or for road surfacing.

Geological facts

Chert has been used by humans since the Stone Age because it fractures like glass, creating razor-sharp edges. It is chemically identical to quartz but differs in its micro-structure.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its curved, shell-like (conchoidal) fracture pattern when broken. Common in limestone outcrops and riverbeds.