sedimentary

Chert (specifically Jasper or Flint variant)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Brown, reddish-brown, or dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Brown, reddish-brown, or dark grey
Luster: Waxy to dull

Identified July 1, 2026More sedimentary →

Explore Chert (specifically Jasper or Flint variant) 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: Brown, reddish-brown, or dark grey; 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 (like radiolaria or diatoms) or by chemical precipitation from silica-rich fluids in sedimentary basins. These rocks can date from the Archean to the Cenozoic.

Uses & applications

Historically used for stone tools and starting fires (flint); currently used in jewelry (as jasper), as a construction aggregate, and for landscaping.

Geological facts

Due to its conchoidal fracture, chert breaks with very sharp edges, making it the primary material for prehistoric arrowheads and spear points. It is virtually insoluble in most chemicals except hydrofluoric acid.

Field identification & locations

Identify by its 'shell-like' conchoidal fracture, its inability to be scratched by a steel knife, and its waxy appearance. Commonly found in limestone or chalk beds as nodules or layers.