sedimentary
Chert / Flint
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Cream, tan, grey, or white (translucent to opaque); Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Cream, tan, grey, or white (translucent to opaque)
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Cream, tan, grey, or white (translucent to opaque); Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. Common in limestone or chalk beds, with ages ranging from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons (arrowheads/knives) due to sharp edges; currently used for road ballast, building materials, and as strike-stones for fire-starting.
Geological facts
Because it breaks with a conchoidal (shell-like) fracture, it produces edges sharper than a surgical scalpel. It was one of the most vital resources for prehistoric humans globally.
Field identification & locations
Identify by its waxy texture, inability to be scratched by a steel knife, and sharp, curved fracture patterns. Found globally in riverbeds or eroding out of limestone cliffs.
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