sedimentary

Banded Chert

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on the Mohs scale; Color: Multi-colored bands (tan, white, grey); Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Multi-colored bands (tan, white, grey)
Luster: Waxy to vitreous

Identified June 29, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on the Mohs scale; Color: Multi-colored bands (tan, white, grey); Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolaria) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (knapping); currently used for jewelry (cabochons), aquarium gravel, and road construction.

Geological facts

Chert was a primary material for prehistoric humans to create arrowheads and scrapers because it breaks with incredibly sharp edges. Banded chert is often confused with agate, but chert is opaque while agate is translucent.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and its tendency to break into smooth, curved surfaces (conchoidal fracture). Commonly found in limestone and dolomite formations.