sedimentary
Chert (Cherty Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically gray, brown, or tan with waxy luster; Crystal Structure: Microcrystalline; Cleavage: None (systemic conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- typically gray, brown, or tan with waxy luster
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: typically gray, brown, or tan with waxy luster; Crystal Structure: Microcrystalline; Cleavage: None (systemic conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often dated from the Paleozoic to Mesozoic eras.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used in construction aggregate, road surfacing, and as a low-cost gemstone for tumbling or lapidary practice.
Geological facts
Chert exhibits conchoidal fracture, meaning it breaks like glass. It was one of the most vital materials for early humans to create arrowheads and scrapers. Some varieties including 'Jasper' and 'Agate' are essentially colorful forms of chert.
Field identification & locations
Identify in the field by its smooth, waxy feel and the way it produces scalloped, razor-sharp edges when chipped. It is commonly found in riverbeds, glacial till, and embedded in limestone outcrops. It will scratch glass easily.
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