sedimentary

Chert (Flint)

Microcrystalline quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Dark blue, grey, or black with conchoidal fracture. Luster: Waxy to vitreous. Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony). Cleavage: None, breaks with a sharp conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 7 on Mohs scale
Color: Dark blue, grey, or black with conchoidal fracture
Luster: Waxy to vitreous

Identified August 6, 2026More sedimentary →

Explore Chert (Flint) in the encyclopedia →

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 diagenesis of siliceous oozes from the remains of marine organisms like diatoms or radiolarians, or through the replacement of limestone or chalk by silica-rich groundwater in marine environments over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and fire-starting (striking against steel). Today used for decorative landscaping, gravel, and occasionally lapidary arts.

Geological facts

Chert and flint are essentially the same material; the term 'flint' is often used specifically for darker varieties found in chalk, while 'chert' is used for occurrences in limestone.

Field identification & locations

Identified by its waxy luster, hardness that scratches glass, and sharp conchoidal fracture edges. Commonly found embedded as nodules within sedimentary rock formations such as limestone and chalk worldwide.