sedimentary
Chert (Grey Chert)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dull grey, tan, or brown; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Dull grey, tan, or brown
- Luster
- Waxy to vitreous
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: Dull grey, tan, or brown; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic); Cleavage: None (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 occurring as nodules or bedded deposits throughout the Paleozoic to Mesozoic eras.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as road aggregate, in abrasive manufacturing, and occasionally as a decorative landscape stone.
Geological facts
Because it breaks with a conchoidal fracture like glass, it was one of the most important minerals for prehistoric tool making. It is very resistant to chemical weathering and often remains in soil long after the surrounding limestone has dissolved.
Field identification & locations
Identify in the field by its hardness (it can scratch glass and steel), its smooth waxy surface, and shell-like (conchoidal) fracture patterns. Frequently found in riverbeds or eroding out of limestone outcrops in the Midwest and Southern United States.
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