sedimentary

Chert (or Chalcedony)

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Brownish-tan with semi-translucent areas; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 7 Mohs
Color: Brownish-tan with semi-translucent areas
Luster: Waxy to vitreous

Identified May 21, 2026More sedimentary →

Explore Chert (or Chalcedony) 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; Color: Brownish-tan with semi-translucent areas; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7.

Formation & geological history

Formed by the precipitation of silica from groundwater or as a biochemical specimen from the remains of silica-shelled organisms in marine environments. Often found in nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (flintknapping); currently used in road surfacing, construction aggregates, and occasionally as lapidary material for jewelry.

Geological facts

Chert is one of the most durable rocks and was essential to early human survival for making spearheads and arrowheads because of its sharp, conchoidal fracture edges.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and its tendency to break into smooth, curved surfaces. Common in riverbeds and sedimentary outcrops.