sedimentary
Chert (Limestone/Flint variant)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-tan/buff; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Grayish-tan/buff
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-tan/buff; Luster: Waxy to dull; 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 by the chemical replacement of limestone/carbonate rock by silica-rich fluids. Common in Precambrian to Cenozoic strata.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp edges when broken. Today used as road aggregate and occasionally as jewelry in the form of jasper or flint.
Geological facts
Chert specimens with high luster and specific colors are often called Jasper, while dark varieties are known as Flint. It was one of the most important resources for prehistoric humans globally.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its characteristic shell-like (conchoidal) fracture pattern when chipped. Found in bedded layers within limestone or as nodules.
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