sedimentary
Chert (Nodule)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale). Color: Gray, tan, and brown with waxy luster. Structure: Microcrystalline/Cryptocrystalline. Features: Conchoidal fracture (breaks with curved surfaces like glass); high density.
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, and brown with waxy luster
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Physical properties
Hardness: 7 (Mohs scale). Color: Gray, tan, and brown with waxy luster. Structure: Microcrystalline/Cryptocrystalline. Features: Conchoidal fracture (breaks with curved surfaces like glass); high density.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine or groundwater environments. Often found as nodules within limestone or chalk beds. Geological age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Currently used in road construction, as an abrasive, and sometimes in landscaping or low-end lapidary jewelry.
Geological facts
Chert has a unique property where it can create sparks when struck against steel, leading to its historical use as 'flint' for fire-starting and in flintlock firearms.
Field identification & locations
Identify in the field by its hardness (it should scratch glass), waxy feel, and smooth curved edges where broken. Commonly found in riverbeds, limestone outcrops, and gravel pits.
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