sedimentary
Chert (Brown Variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Dull brown to tan; Luster: Waxy to sub-glassy; Crystal structure: Cryptocrystalline (hexagonal system at microscopic level); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Dull brown to tan
- Luster
- Waxy to sub-glassy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Dull brown to tan; Luster: Waxy to sub-glassy; Crystal structure: Cryptocrystalline (hexagonal system at microscopic level); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed by the accumulation of siliceous remains of marine organisms or by chemical precipitation from silica-rich groundwater within limestone or chalk beds. It can date from the Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools (lithics) due to its sharp edges when broken. High-quality varieties are used in jewelry and lapidary work. Crushed chert is used as a sub-base for roads and in concrete.
Geological facts
Chert is so hard that it can strike sparks against steel, which made it essential for flintlock firearms and early fire-starting kits. Brown chert is often referred to as 'jasper' if it is opaque and highly aesthetic.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture pattern and its inability to be scratched by a steel knife. It is common in riverbeds and limestone outcrops worldwide.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary