sedimentary

Chert (Jasper variation)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Reddish-brown, tan, and cream mottling; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.58–2.91

Hardness: 6
Color: Reddish-brown, tan, and cream mottling
Luster: Dull to waxy

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from hydrothermal fluids in sedimentary environments. Variations like this often form in nodules within limestone or as bedded deposits.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used for lapidary work, jewelry (cabochons), and as an ornamental landscaping stone.

Geological facts

Chert is so hard it can strike sparks from steel, causing it to be used historically as 'flint' for fire-starting and flintlock firearms. The red coloration is typically due to iron oxide (hematite) inclusions.

Field identification & locations

Identify in the field by its characteristic conchoidal (shell-like) fracture patterns and ability to scratch glass. Commonly found in riverbeds, desert pavements, and weathered limestone outcrops worldwide.

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