sedimentary

Chert (Quartz Variety)

Silicon Dioxide (SiO2)

Hardness: 7 on the Mohs scale; Color: Tan, beige, or white (can vary); Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7

Hardness: 7 on the Mohs scale
Color: Tan, beige, or white (can vary)
Luster: Waxy to dull

Identified March 23, 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 accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in groundwater. This specimen likely originates from limestone or chalk beds and can range from 10 to hundreds of millions of years old.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges when broken. Today, it is used in road construction, as an abrasive, and sometimes in low-cost jewelry or as a decorative 'river rock'.

Geological facts

Chert is so hard it can scratch glass. It was one of the most vital materials for prehistoric humans for fire-starting (when struck against steel or pyrite) and tool-making.

Field identification & locations

Identify in the field by its waxy texture and shell-like (conchoidal) curved breaks. It is very common in gravel pits and riverbeds. For collectors, look for pieces with interesting patterns or colors.