sedimentary
Chert (specifically Tan Chert or Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brown, or buff; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, or buff
- Luster
- Dull to waxy
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, or buff; Luster: Dull to waxy; 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 radiolaria or diatoms) or by chemical precipitation from silica-rich fluids within limestone or chalk beds. Often Paleozoic or Mesozoic in age.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Currently used in road surfacing, as a gemstone (Jasper/Agate variants), and for landscaping.
Geological facts
Chert breaks with a conchoidal fracture, creating sharp edges which is why it was the primary material for prehistoric arrowheads and spear tips. It is extremely resistant to chemical weathering.
Field identification & locations
Identify in the field by its smooth, waxy feel and the way it breaks into curved, shell-like flakes. It will easily scratch glass. Found globally in nodules or layered beds within carbonate rocks.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary