sedimentary

Chert / Chalcedony Nodule

Silicon Dioxide (SiO2)

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 →

Explore Chert / Chalcedony Nodule in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

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.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Shale

Shale (clastic sedimentary rock)

sedimentary

Brown Sandstone (River Rock)

Arenite

sedimentary

Shale

Argillaceous sedimentary rock

sedimentary