sedimentary
Chert (Jasper/Flint variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Grayish-brown with tan inclusions; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.65
- Hardness
- 6
- Color
- Grayish-brown with tan inclusions
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Grayish-brown with tan inclusions; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical replacement of limestone/dolomite. This specimen appears water-worn, likely from a riverbed or coastal environment.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp edges when broken. Today used in landscaping, road construction, and as aquarium stones.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the first materials humans used to create fire (when struck against steel or pyrite) and tools during the Stone Age.
Field identification & locations
Identify by its extreme hardness and smooth, shell-like (conchoidal) fracture surface. It is very common in gravel beds and limestone outcroppings globally.
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