sedimentary
Chert (specifically Gray Chert)
Chert (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and brownish-yellow; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and brownish-yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and brownish-yellow; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or through chemical precipitation in marine or groundwater environments. Can vary in age from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for decorative gravel, landscaping, and as a component in construction aggregate.
Geological facts
Chert is chemically identical to quartz but has a much finer crystal structure. When it occurs in chalk or marl, it is specifically referred to as flint.
Field identification & locations
Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is commonly found in stream beds or as nodules within limestone layers.
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