sedimentary

Chert (Quartz)

Silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: cream to tan with iron staining; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, conchoidal fracture; Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: cream to tan with iron staining
Luster: waxy to dull

Identified July 15, 2026More sedimentary →

Explore Chert (Quartz) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 (Mohs scale); Color: cream to tan with iron staining; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, conchoidal fracture; Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (such as diatoms or radiolarians) or chemical precipitation in marine or freshwater environments. This specimen likely dates from the Phanerozoic eon.

Uses & applications

Historically used for stone tools and start-fires; currently used as construction aggregate, road base, and occasionally for decorative landscaping or lapidary work.

Geological facts

Chert is so hard it can scratch glass and steel. It was the primary material for arrowheads and scrapers used by prehistoric humans because of its sharp, glass-like fracture edges.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness, and smooth, curved (conchoidal) fracture surfaces. Common in limestone formations globally. Collectors should look for nodules in stream beds.