sedimentary
Chert
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 Mohs scale; Color: Grey, tan, and brown; Luster: Waxy to dull; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Grey, tan, and brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Grey, tan, and brown; Luster: Waxy to dull; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich microfossils or through chemical precipitation in marine environments; age varies from Precambrian to modern times.
Uses & applications
Historically used for making stone tools like arrowheads; currently used as construction aggregate or in lapidary work.
Geological facts
Chert is so hard it can create sparks when struck against steel, which made it a vital material for ancient survival and early fire-starting tools.
Field identification & locations
Check for a smooth, waxy surface and conchoidal (shell-like) fractures. It will easily scratch glass and is found globally in limestone and chalk deposits.
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