sedimentary
Chert (Jasper/Mudstone variety with Oxidation)
Silicon dioxide (SiO2)
Hardness: 6.5-7 (Mohs), Color: Tan, brown, and yellow-orange (due to iron oxides), Luster: Dull to waxy, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (conchoidal fracture).
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Tan, brown, and yellow-orange (due to iron oxides), Luster: Dull to waxy, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. The distinct layering and 'rind' are results of chemical weathering and oxidation (limonite staining) over geologic time.
Uses & applications
Historically used for stone tools/arrowheads. Today used for landscaping, as a minor gemstone (jasper), and for fire-starting (flint).
Geological facts
The yellow-orange outer layer is often called a 'weathering rind,' caused by the oxidation of iron-bearing minerals within the rock once exposed to oxygen and water.
Field identification & locations
Look for a smooth, waxy surface on broken edges and a sharp, shell-like (conchoidal) fracture pattern. Commonly found in riverbeds and limestone deposits.
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