sedimentary
Yellow Chert (Jasper)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7.0 (Mohs scale); Color: Opaque yellow to mustard brown; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Opaque yellow to mustard brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7.0 (Mohs scale); Color: Opaque yellow to mustard brown; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms) or chemical precipitation in marine or groundwater environments. This specimen likely dates from any period between the Precambrian to Cenozoic.
Uses & applications
Commonly used for lapidary work (cabochons), historical tool-making (arrowheads/scrapers), and as a landscaping stone.
Geological facts
Yellow chert is often referred to as Yellow Jasper when it is opaque and highly aesthetic. Because it breaks with a conchoidal fracture, it was one of the most important materials for early humans to create sharp cutting tools.
Field identification & locations
Identify by its 'glassy' conchoidal fracture pattern even though it appears earthy, its inability to be scratched by a steel knife, and its opaque nature. Found globally in limestone formations or as river-worn cobbles.
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