sedimentary

Chert / Chalcedony Nodule

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: White, cream, tan, light grey, to pale yellow. Luster: Waxy to vitreous (glassy). Crystal Structure: Microcrystalline/Cryptocrystalline trigonal quartz. Fracture: Conchoidal with sharp edges.

Hardness: 6
Color: White, cream, tan, light grey, to pale yellow
Luster: Waxy to vitreous (glassy)

Identified July 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich fluids or biological oozes (such as radiolarians or diatoms) in sedimentary environments, often replacing carbonate rocks like limestone or chalk. Commonly found in Marine Cretaceous or Tertiary sedimentary deposits worldwide.

Uses & applications

Historically used for stone tools, arrowheads, and spark-striking flints. Modern uses include lapidary arts, tumbling, specimen collecting, and decorative rock carving.

Geological facts

Chert and chalcedony were among the most critical resources for prehistoric humans due to their ability to fracture with predictable, razor-sharp conchoidal edges.

Field identification & locations

Look for a chalky outer weathered rind (cortex) covering a dense, fine-grained, translucent to opaque quartz interior that easily scratches glass and steel.