sedimentary
Chert (with Limonite staining)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: White/Grey with yellow-brown staining; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- White/Grey with yellow-brown staining
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: White/Grey with yellow-brown staining; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments. The yellow staining is likely Limonite, a hydrated iron oxide formed via weathering.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp fracture edges. Today it is used in road construction, as an abrasive, and sometimes in landscaping.
Geological facts
Chert is so hard it can scratch glass and steel. Certain varieties like flint have been used for thousands of years to create fire by striking them against steel.
Field identification & locations
Identify by its extreme hardness and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in limestone or chalk beds as nodules or layers throughout the world.
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