sedimentary
Chert (and associated Sedimentary rocks)
Microcrystalline Silica (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brown, or black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brown, or black
- 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: Gray, tan, brown, or black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or by the chemical replacement of limestone/dolomite by silica-rich fluids. Usually found in Phanerozoic age strata.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to sharp edges; currently used for road base, decorative landscaping, and as a raw material for silicon-based products.
Geological facts
Chert is so hard it can scratch glass and steel. Flint is a high-quality variety of chert. It has been used by humans for millions of years to start fires and create weaponry.
Field identification & locations
Identify in the field by its very hard surface, waxy texture, and distinctive 'shell-like' shell-like (conchoidal) fractures. Often found in nodules within limestone layers or as river pebbles.
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 (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary