sedimentary
Chert (Iron-stained)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brownish-red to tan due to iron oxides, Luster: Dull to waxy, Crystal Structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Brownish-red to tan due to iron oxides, Luster: Dull to waxy, Crystal Structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in marine limestone and dolomite formations.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include road aggregate, jewelry (when colorful/Jasper), and decorative landscaping.
Geological facts
Chert is so hard it can spark when struck against steel. It has been used by humans for hundreds of thousands of years to create sharp-edged tools and fire-starting kits.
Field identification & locations
Identify by its 'conchoidal' (shell-like) fracture patterns and extreme hardness (it will scratch glass). Often found as nodules within limestone or as pebbles in riverbeds.
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