sedimentary
Chert (Flint/Gray Chalcedony)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Gray to brownish-gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray to brownish-gray
- 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 (Mohs scale); Color: Gray to brownish-gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation in marine environments and limestone cavities. Age varies widely from Precambrian to Cenozoic.
Uses & applications
Historically used for making stone tools and starting fires; currently used as filler in construction, decorative landscaping, and occasionally for cabochon jewelry or flintknapping art.
Geological facts
Chert and flint were among the first materials used by early humans to create sophisticated tools due to their predictable fracturing patterns. Gray chert is often part of the 'Lake Superior Agate' family when found in the American Midwest.
Field identification & locations
Identify in the field by looking for smooth, shell-like (conchoidal) fractures and its ability to scratch glass. Commonly found in riverbeds, glacial till, and embedded in limestone/dolomite outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary