sedimentary

Chert (Jasper/Flint variety)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 7 Mohs
Color: Brown, tan, reddish-brown
Luster: Waxy to dull

Identified July 13, 2026More sedimentary →

Explore Chert (Jasper/Flint variety) 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: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed by the precipitation of silica from groundwater or the accumulation of siliceous biological remains (like radiolarians) in sedimentary basins. Often occurs as nodules in limestone or chalk.

Uses & applications

Historically used for stone tools/weapons; currently used in jewelry (as jasper), landscaping, and as a component in construction aggregate.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use as 'flint' in strike-a-light sets and flintlock firearms.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture, waxy texture, and extreme hardness. It won't be scratched by a knife blade. Found in riverbeds and sedimentary outcrops worldwide.