sedimentary
Chert (Flint/Jasper variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish-yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, or grayish-yellow
- 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: Tan, brown, or grayish-yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of siliceous skeletal remains (diatoms/radiolarians) in marine environments. These specimens often originate in limestone or chalk beds from various geological eras, including the Cretaceous.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in road construction as aggregate, as a component in certain ceramics, and as decorative gravel.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture creates edges sharper than a surgical scalpel. It is also famous for its use in fire-starting as 'flint' when struck against steel.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its characteristic shell-like (conchoidal) fracture pattern when broken. It is commonly found in riverbeds, agricultural fields, or eroding out of limestone outcrops worldwide.
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