sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2) with Iron Oxide impurities
Hardness: 6.5-7 (Mohs), Color: Reddish-brown to yellow-ochre, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Reddish-brown to yellow-ochre, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed primarily from the precipitation of silica-rich fluids or the accumulation of siliceous remains of microorganisms (like radiolaria) in marine environments. Iron oxide inclusions provide the reddish color.
Uses & applications
Historically used for stone tools and arrowheads. Currently used as a gemstone in lapidary work, jewelry, and as decorative gravel.
Geological facts
Red chert is often referred to as Jasper. It was one of the most important minerals for early humans due to its ability to break with sharp edges for tools.
Field identification & locations
Look for a waxy luster and smooth, curved (conchoidal) breaks. It is commonly found in riverbeds or as nodules within limestone or shale. It will scratch glass easily.
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