sedimentary
Chert Nodule (Flint)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or gray with a lighter weathered cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or gray with a lighter weathered cortex
- Luster
- Waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or gray with a lighter weathered cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the replacement of limestone or chalk by silica-rich fluids, often accumulating around organic nuclei. These typically date from the Cretaceous to Jurassic periods in marine environments.
Uses & applications
Historically used for stone tools and starting fires; currently used as an abrasive, in road construction, and as a collector's specimen.
Geological facts
Chert is so hard it can scratch steel. When broken, it produces sharp edges which made it the primary material for arrowheads and spear points for thousands of years.
Field identification & locations
Identify in the field by its distinctive 'rind' or cortex and its smooth, shell-like (conchoidal) fracture surface. Frequently found in limestone outcrops or as rounded pebbles in riverbeds.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary