sedimentary
Chert (specifically White Chert or Flint)
Microcrystalline or cryptocrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: White to light grey with tan patches; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- White to light grey with tan patches
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light grey with tan patches; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation from hydrothermal fluids in sedimentary basins. Primarily found in limestone or chalk beds as nodules or layers.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp edges; currently used in construction aggregate, road surfacing, and as a raw material in glass manufacturing.
Geological facts
Chert has been one of the most important minerals for human development, as it produces a razor-sharp edge when broken (knapped) and can create sparks when struck against steel to start fires.
Field identification & locations
Identify by its extremely smooth, curved (conchoidal) fracture surfaces and the fact that it can easily scratch glass. Found globally in limestone outcrops or as smooth river stones.
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