sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, or earthly pink; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline (Trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Reddish-brown, tan, or earthly pink
Luster: Waxy to dull

Identified February 17, 2026More sedimentary →

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 precipitation of silica in sedimentary environments, often replacing organic matter or calcium carbonate. This water-rounded nodule likely originated in marine limestone beds and was later weathered out. Geological age varies widely from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to sharp fracture edges. Today it is used in road construction as aggregate, as a component in certain ceramics, and as a durable lapidary material for tumbled stones or beads.

Geological facts

Chert is chemically identical to quartz but has a different internal structure consisting of microscopic crystals. Varieties of reddish chert are often referred to as Jasper. It was one of the first minerals utilized by prehistoric humans for technology.

Field identification & locations

Identify in the field by its smooth, waxy texture and characteristic conchoidal (shell-like) fractures. It is commonly found in riverbeds as rounded pebbles or embedded in limestone cliffs. Collectors should look for signs of translucency at thin edges and high scratch resistance against steel.