sedimentary
Chert (often called Flint or Jasper)
Cryptocrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) on the ocean floor, or through chemical precipitation in groundwater. It can found in nodules within limestone or as bedded deposits.
Uses & applications
Historically used for stone tools and starting fires; currently used as a gemstone (when colorful like jasper), in road construction, and as a component in glass making.
Geological facts
Because it breaks with a conchoidal fracture, it creates edges sharper than a surgeon's steel scalpel, making it the primary material for prehistoric arrowheads and spear tips.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and smooth, shell-like (conchoidal) fracture marks. Look for it in limestone or chalk outcrops.
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