sedimentary

Chert (Flint nodule)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 7 (Mohs scale); Color: White weathered exterior (cortex) with a gray/black waxy interior; Luster: its waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Luster: its waxy to vitreous

Identified April 11, 2026More sedimentary →

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 debris (like sponge spicules or radiolarians) or chemical precipitation in sedimentary environments like limestone or chalk. Often found as nodules within host rock.

Uses & applications

Historically used for stone tools and weapons. Currently used as road aggregate, in glass manufacturing, and as 'flint' in fire-starting kits.

Geological facts

Chert breaks with a conchoidal fracture, creating extremely sharp edges. It was the primary material for arrowheads and scrapers during the Stone Age. The white outer layer is called a 'cortex,' caused by chemical weathering.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its waxy internal texture when broken, and its characteristic curved, shell-like fracture pattern. Often found in riverbeds or eroding out of limestone cliffs.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone (Quartz-rich)

Arenite (SiO2)

sedimentary

Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

sedimentary