sedimentary
Chert (Yellow Jasper/Flint)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs. Color: Tan, yellow-brown, or ochre. Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Tan, yellow-brown, or ochre
- Luster
- Dull to waxy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 Mohs. Color: Tan, yellow-brown, or ochre. Luster: Dull to waxy. Crystal structure: 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 hydrothermal fluids. This specimen appears water-worn, likely from an alluvial or glacial deposit.
Uses & applications
Historically used for stone tools and fire-starting (flint). Currently used as decorative landscaping rock, jewelry (when polished as jasper), and as a gemstone for collectors or 'pocket stones'.
Geological facts
Chert breaks with a conchoidal fracture, creating razor-sharp edges which made it the primary material for arrowheads and spear points in the Stone Age. It is chemically identical to quartz but has a much finer grain.
Field identification & locations
Identify in the field by its wax-like texture, smoothness, and 'clinking' sound when struck with metal. It cannot be scratched by a steel knife. Common in limestone regions and creek beds globally.
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