sedimentary
Chert (White Chert or Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs scale; Color: White to off-white; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic fibers); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
- Hardness
- 6
- Color
- White to off-white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs scale; Color: White to off-white; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic fibers); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons due to its sharp conchoidal fracture. Modernly used in road construction, as jewelry (if colorful), and as a sparking source in flint-and-steel fire starting.
Geological facts
Chert is so durable it often survives the weathering of its host limestone, leaving behind nodules on the ground. It has been used by humans for hundreds of thousands of years for arrowheads and scrapers.
Field identification & locations
Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and its shell-like (conchoidal) fracture pattern. Found globally in sedimentary basins.
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