sedimentary
Chert (White/Light Tan)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white to light tan; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (hexagonal system at microscopic level); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7.
- Hardness
- 7 on Mohs scale
- Color
- Off-white to light tan
- 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 on Mohs scale; Color: Off-white to light tan; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (hexagonal system at microscopic level); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids within sedimentary rock layers, often replacing limestone or dolostone. Generally found in marine or hydrothermal environments across various geological ages.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modernly used as a flux in steel production, road ballast, or as a component in construction abrasives. Rarely used in jewelry except as tumble-polished stones.
Geological facts
Chert has a unique breaking pattern known as conchoidal fracture, similar to glass. It was one of the most important raw materials for early humans; 'flint' is a dark variety of chert. It is extremely chemically stable and resistant to weathering.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass and steel), its sharp, shell-like fracture edges, and its smooth, waxy feel. Commonly found in riverbeds, limestone quarries, and coastal cliffs. Collectors should look for worked edges that indicate it may be a debitage flake from prehistoric tool-making.
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