sedimentary
Chert (Iron-stained variant)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, cream, with reddish-orange iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, cream, with reddish-orange iron staining
- 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: Tan, cream, with reddish-orange iron staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or groundwater environments. Can range from Precambrian to Cenozoic in age.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; modernly used as road aggregate, in landscaping, and as a low-cost lapidary material for tumbling.
Geological facts
Because of its hardness and conchoidal fracture, it was the primary material used by prehistoric humans to create arrowheads, scrapers, and knives. It is also known as 'flint' when found in chalk or marl.
Field identification & locations
Identify in the field by its hardness (it scratches glass easily) and its shell-like (conchoidal) breakage patterns. Often found as nodules in limestone or as distinct bedded layers in riverbeds.
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