sedimentary
Yellow Chert (Chert/Jasper)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Opaque yellowish-brown to tan, Luster: Waxy to vitreous, Crystal Structure: Microcrystalline/Cryptocrystalline trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Opaque yellowish-brown to tan, Luster: Waxy to vitreous, Crystal Structure: Microcrystalline/Cryptocrystalline trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation from hydrothermal fluids in sedimentary environments. Common in marine limestone environments.
Uses & applications
Used historically for stone tools due to conchoidal fracturing; modern uses include decorative landscaping, lapidary work (tumbling/polishing), and as an abrasive in some industrial processes.
Geological facts
Chert was one of the first materials used by early humans to create sharp-edged tools and arrowheads. Yellow varieties often derive their color from iron oxide impurities (goethite).
Field identification & locations
Identify by its waxy texture, lack of visible crystals, and sharp, shell-like fracture edges. Frequently found in riverbeds, glacial tills, or embedded in limestone beds. It will scratch glass easily.
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