sedimentary

Chert (Brown Chert / Flint)

Silicon Dioxide (SiO2)

Hardness: 7 Mohs scale; Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 Mohs scale
Color: Brown, tan, reddish-brown
Luster: Waxy to dull

Identified July 5, 2026More sedimentary →

Explore Chert (Brown 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 accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater. It often forms as nodules or beds within limestone or chalk formations. Common in Paleozoic and Mesozoic strata.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges when broken. Today used in gravel production, road surfacing, and as a decorative specimen for collectors.

Geological facts

Chert was one of the most important materials for early humans; its ability to produce sharp, glass-like edges through a process called knapping revolutionized tool-making. 'Flint' is a variety of chert, often darker in color.

Field identification & locations

Identify by its extremely smooth, waxy feel and characteristic curved, shell-like (conchoidal) fractures. It is harder than steel and will scratch glass. Found globally, especially in areas with eroded limestone outcrops.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary