sedimentary
Chert (Flint)
Chert (Cryptocrystalline variety of Quartz, SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brown, gray, and cream with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, gray, and cream with waxy luster
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale); Color: Tan, brown, gray, and cream with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids. Generally found in marine limestone or dolomite beds as nodules or layers. Can range from Precambrian to Recent geological periods.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modernly used in road construction, as a source for silica in glassmaking, and by survivalists for fire-starting.
Geological facts
Because of its conchoidal fracture, it can be knapped to create edges sharper than a steel scalpel. Native Americans and many ancient cultures traded high-quality chert over thousands of miles.
Field identification & locations
Identify in the field by its very hard, smooth surface that cannot be scratched by steel and its sharp, shell-like (conchoidal) breaks. Often found as hard nodules protruding from softer limestone cliffs.
More like this
Other sedimentary specimens
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