sedimentary

Flint / Chert (or fossiliferous nodule)

Microcrystalline quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Varies from grey, white, brown to yellowish. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline or microcrystalline quartz (chalcedony). Cleavage: None, exhibits conchoidal fracture.

Hardness: 7 on Mohs scale
Color: Varies from grey, white, brown to yellowish
Luster: Waxy to vitreous

Identified August 1, 2026More sedimentary →

Explore Flint / Chert (or fossiliferous nodule) 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 replacement of calcium carbonate by silica-rich solutions in sedimentary environments, often within chalk or limestone formations over millions of years during the Cretaceous period and other geological eras.

Uses & applications

Historically used for making stone tools, arrowheads, and striking fire. Today used for decorative landscaping, gravel, flint knapping hobbies, and historically in flintlock firearms.

Geological facts

Flint and chert are chemically identical, though archaeologists and geologists often use 'flint' to describe material found in chalk formations and 'chert' for varieties found in limestone.

Field identification & locations

Identified by its distinctive conchoidal fracture, sharp edges when broken, waxy luster, and high hardness capable of scratching glass. Commonly found in chalk deposits and river gravels.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Quartz pebble

Silicon dioxide (SiO2)

sedimentary

Generic Pebble / Rock Fragment

Lithic fragment / Weathered rock

sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary