sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, reddish-brown, and tan; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8

Hardness: 6
Color: Brown, reddish-brown, and tan
Luster: Dull to sub-vitreous

Identified March 26, 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 fluids in sedimentary basins or the replacement of limestone. This specimen appears to be a microcrystalline quartz variety formed in marine environments, potentially dating from various geological eras depending on location (commonly Paleozoic/Mesozoic).

Uses & applications

Historically used for stone tools (knapping) due to its conchoidal fracture. Modern uses include abrasives, decorative stones, landscaping, and jewelry when vibrantly colored (as Jasper).

Geological facts

Because of its extreme hardness and ability to hold a sharp edge, chert/flint was one of the most important minerals for early human survival, used for making arrowheads and spear points.

Field identification & locations

Identify in the field by its smooth, waxy feel and characteristic 'scooped out' shell-like (conchoidal) fractures. It will easily scratch glass. Commonly found in nodular form in limestone or as rounded river cobbles.