sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, white, and translucent; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, white, and translucent
Luster: Waxy to dull

Identified June 10, 2026More sedimentary →

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: Gray, tan, white, and translucent; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed by the precipitation of silica from groundwater in sedimentary environments, often replacing organic material or filling cavities in limestone/chalk. Found in formations ranging from Precambrian to recent.

Uses & applications

Historically used for stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as landscaping stone. High-quality colorful pieces are used in jewelry as 'Jasper' or 'Agate'.

Geological facts

Known for its conchoidal fracture which creates razor-sharp edges, making it the primary material for prehistoric arrowheads and spear points. It was also critical for 'flintlock' firearms.

Field identification & locations

Field identification involves checking for a waxy luster and the ability to scratch glass easily. Look for sharp, shell-like (conchoidal) fractures on broken edges. Common in river beds and limestone outcrops.