sedimentary
Chert (Nodule)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: tan, buff, or brown with white weathering rind, Luster: waxy to dull, Crystal Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, buff, or brown with white weathering rind, Luster: waxy to dull, Crystal Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed through the precipitation of silica from groundwater within limestone or chalk beds. Often associated with marine environments from the Paleozoic or Mesozoic eras.
Uses & applications
Used historically for stone tools and fire-starting; currently used as road aggregate, in landscaping, and as a filler in various industrial applications.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create sharp-edged tools like arrowheads and knives due to its predictable fracturing pattern.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and conchoidal (shell-like) fractures. Often found in riverbeds or within limestone outcrops.
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