sedimentary

Chert (variously known as Flint or Microcrystalline Quartz)

Silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, beige, or off-white with iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, beige, or off-white with iron staining
Luster: Waxy to dull

Identified April 11, 2026More sedimentary →

Explore Chert (variously known as Flint or Microcrystalline Quartz) 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 accumulation of silica-rich microfossils (like radiolarians or diatoms) or by the replacement of carbonate minerals in limestone/chalk. Found in formations ranging from Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges; currently used as construction aggregate, road base, and occasionally in lapidary work.

Geological facts

Chert has a unique breaking pattern called conchoidal fracture, which results in smooth, curved surfaces similar to glass. It was one of the most vital materials for stone-age technology.

Field identification & locations

Identify in the field by its hardness (it can scratch glass), its waxy feel, and its curved, shell-like fracture marks. Commonly found as nodules or layers within limestone beds.