sedimentary

Chert (Quartz)

Microcrystalline Silica (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, white, or gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Tan, brown, white, or gray
Luster: Waxy to dull

Identified March 28, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, white, or gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within limestone or chalk beds. Most specimens date from the Precambrian to recent times.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to conchoidal fracturing. Modern uses include road surfacing, jewelry (jasper/agate varieties), and as a silica source in glass manufacturing.

Geological facts

Chert played a vital role in human evolution as one of the primary materials for the Stone Age tool industry. It is extremely resistant to weathering and is often found as nodules within softer rocks like limestone.

Field identification & locations

Identify in the field by its waxy texture and shell-like (conchoidal) curved fractures. It will scratch glass but cannot be scratched by a steel knife. Frequently found in riverbeds or limestone outcrops worldwide.