sedimentary
Chert (Flint/Jasper variety)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Gravity: 2.6-2.7.
Formation & geological history
Formed from the recrystallization of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires (flint). Used today in gravel, road construction, and occasionally as a lapidary material for jewelry if colorful.
Geological facts
Because it breaks with a conchoidal fracture, it creates edges sharper than a surgeon's scalpel. It has been used by humans for hundreds of thousands of years for spear points and arrowheads.
Field identification & locations
Identify by its waxy texture, extreme hardness (it will scratch glass), and the way it chips into curved, shell-like flakes. Frequently found in riverbeds or within sedimentary rock outcrops.
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