sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, reddish-brown with white quartz veins; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Brown, reddish-brown with white quartz veins
Luster: Waxy to dull

Identified June 4, 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 organic remains or chemical precipitation in marine environments. Often found as nodules or bedded deposits within limestone or dolomite; can date back billions of years to the Precambrian.

Uses & applications

Used historically for stone tools and arrowheads due to conchoidal fracture. Currently used for lapidary work, jewelry (beads/cabochons), and as aquarium or landscaping gravel.

Geological facts

Chert was one of the most important minerals for early humans to create sharp cutting tools. Reddish varieties are technically called Jasper, while dark gray or black is called Flint.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and smooth, shell-like fracture surfaces. Frequently found on beaches or in riverbeds where erosion has concentrated harder minerals.