sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, gray, or black; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Brown, gray, or black
Luster: Waxy to vitreous

Identified May 24, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, gray, or black; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments like limestone or chalk beds. Most specimens date from the Phanerozoic eon.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road surfacing, as grinding media, and by hobbyists for lapidary work.

Geological facts

Flint is a variety of chert that occurs primarily in chalk or marly limestone. It was the primary material for human tools for over two million years and was crucial for early survival due to its ability to create sharp edges.

Field identification & locations

Look for a smooth, waxy surface and sharp, curved (conchoidal) edges where broken. Often found as nodules within limestone or as pebbles in riverbeds and on beaches.