sedimentary

Flint

Silicon dioxide (Microcrystalline quartz, SiO2)

Hardness: 7 on the Mohs scale. Color: Brownish-gray with lighter cortex. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline / microfibrous quartz (chalcedony). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 7 on the Mohs scale
Color: Brownish-gray with lighter cortex
Luster: Waxy to vitreous

Identified August 5, 2026More sedimentary →

Explore 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 as nodules and masses in sedimentary rocks, primarily chalk and marine limestones, through the replacement of calcium carbonate by silica-rich solutions during the Cretaceous period.

Uses & applications

Historically used for making stone tools, arrowheads, and firearm ignition (flintlocks). Currently used in abrasives, ceramics, and as decorative landscape gravel.

Geological facts

Flint produces sparks when struck against steel due to its high hardness and brittle conchoidal fracturing, which was crucial for fire-making and weaponry throughout human history.

Field identification & locations

Easily identified in the field by its smooth, bulbous weathering crust (cortex), sharp conchoidal edges when broken, and waxy luster. Commonly found along chalk cliffs and beaches, such as the white cliffs of Dover.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Quartz pebble

Silicon dioxide (SiO2)

sedimentary

Generic Pebble / Rock Fragment

Lithic fragment / Weathered rock

sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary