sedimentary

Chert Pebble

Silicon dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Grayish-brown with dark bands; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Grayish-brown with dark bands
Luster: Waxy to vitreous

Identified June 2, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Grayish-brown with dark bands; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed by the accumulation of siliceous remains of marine organisms (like diatoms or radiolaria) or through chemical precipitation in sedimentary environments. Common throughout all geological ages.

Uses & applications

Historically used for stone tools/arrowheads due to its sharp edges; used today as decorative gravel, in road construction, and occasionally as minor gemstones (jasper/agate variants).

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates edges sharper than a surgeon's scalpel. Flint is a well-known variety of chert.

Field identification & locations

Identified in the field by its hardness (scratches glass), waxy luster, and smooth, curved fracture surfaces. Commonly found in riverbeds, glacial tills, and limestone outcrops.