sedimentary
Chert (Common Chert)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brown, white, and gray; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, white, and gray
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, brown, white, and gray; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed primarily through the precipitation of silica in marine environments or by the replacement of carbonate rocks by silica-rich fluids. It is found in geological strata ranging from Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modern uses include road base construction material, gravel, and occasionally as a base for lapidary work.
Geological facts
Chert has been used by humans for over a million years because its conchoidal fracture creates sharp edges. 'Flint' is a variety of chert, typically found in chalk or marly limestone.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), waxy feel on fresh surfaces, and smooth, shell-like (conchoidal) fractures. It is commonly found as nodules in limestone or as bedded deposits.
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