sedimentary
Chert (specifically White Chert or Novaculite)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale); Color: White to off-white; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7
- Hardness
- 7 (Mohs scale)
- Color
- White to off-white
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: White to off-white; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7
Formation & geological history
Formed from the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or chemical precipitation of silica in marine environments. It is often found in nodules within limestone or shale layers.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp edges. Modernly used in geological road fill, as a sharpening stone (Novaculite), and in construction aggregates.
Geological facts
Chert is so hard it can create sparks when struck against steel. Novaculite, a dense form of chert from Arkansas, is considered one of the finest natural honing stones for sharpening blades in the world.
Field identification & locations
Identify by its 'flint-like' behavior: it breaks with smooth, shell-like (conchoidal) curves leaving very sharp edges. It cannot be scratched by a knife. Commonly found in stream beds or limestone outcrops across North America.
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