sedimentary
Chert (Yellow Jasper variant)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Yellow-brown (ochre); Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Yellow-brown (ochre)
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Yellow-brown (ochre); Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the precipitation of silica-rich fluids in sedimentary environments or by the accumulation of siliceous skeletal remains (like diatoms or radiolarians). It can also occur as replacement nodules in limestone. Geological age varies widely from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and arrowheads due to sharp edges when fractured. Modernly used as decorative landscaping stone, in lapidary work (jewelry), and as a raw material in some ceramic glazes.
Geological facts
Jasper is essentially impure chert colored by iron oxides. Because it breaks with a conchoidal fracture (smooth, curved surfaces), it was one of the most important materials for early human tool-making alongside flint.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its sharp, shell-like fracture edges. It is commonly found globally in sedimentary basins, riverbeds, and as nodules in limestone or chalk. Collectors look for uniform color and lack of internal cracks.
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