sedimentary

Chert (Jasper/Chalcedony)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Tan, beige, or yellowish-brown
Luster: Waxy to dull

Identified April 7, 2026More sedimentary →

Explore Chert (Jasper/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 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); 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 via chemical precipitation in sedimentary basins. It often replaces original carbonate materials in limestone.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used in construction aggregate and as a semi-precious gemstone in jewelry when it exhibits unique colors.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture produces razor-sharp edges. It is chemically identical to quartz but has a different microscopic structure.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found as nodules in limestone or as smooth river pebbles.