sedimentary
Chert (White Chert)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: White to off-white; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; 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; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or the chemical precipitation of silica in sedimentary basins. Most North Dakota cherts are from the Cenozoic or Paleozoic eras.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp edges; currently used for landscaping, road base, or as interesting lapidary specimens.
Geological facts
Near Minot, ND, chert and flint are commonly found in glacial till and river gravels. This specimen shows significant water-wear and weathering, giving it its rounded, pitted appearance.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel blade) and its smooth, shell-like (conchoidal) fracture surfaces. Very common in the North Dakota plains and gravel pits.
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