sedimentary
Chert (Yellow or Tan variety)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, yellow, or light brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, yellow, or light brown
- 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, yellow, or light brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich micro-organisms (like radiolarians or diatoms) on the ocean floor or through chemical precipitation in groundwater. It can range from Precambrian to Cenozoic in age.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; modernly used in road construction as aggregate, in decorative landscaping, and occasionally as semi-precious gemstones (jaspers).
Geological facts
Chert is so durable that it often remains behind as 'residual soil' after the surrounding limestone or more soluble rocks have weathered away. It was one of the most vital resources for prehistoric humans to create arrowheads and scrapers.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture patterns, extreme hardness (it will scratch glass and steel), and smooth, waxy texture. Commonly found as nodules or layers within limestone or dolomite beds.
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