sedimentary
Chert (Jasper/Chaldcedony)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, and grey with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, tan, and grey with waxy luster
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, and grey with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. Often found as nodules or pebbles in riverbeds and glacial till.
Uses & applications
Historical use for stone tools and flintknapping. Modern use in lapidary work, jewelry (tumbled stones), and as decorative gravel.
Geological facts
Chert is so hard it can scratch steel. It was one of the most important minerals for early humans because its conchoidal fracture produces razor-sharp edges for tools.
Field identification & locations
Identify by its waxy luster, smoothness, and the way it breaks into curved, shell-like flakes. Found globally in riverbeds and areas with limestone deposits.
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