sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Mohs hardness: 7; Color: Yellow-brown to tan; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6
- Hardness
- 7
- Color
- Yellow-brown to tan
- Luster
- Waxy to dull
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Physical properties
Mohs hardness: 7; Color: Yellow-brown to tan; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6
Formation & geological history
Formed from the precipitation of silica-rich fluids or the accumulation of siliceous remains (like diatoms or radiolarians) in sedimentary environments. Its weathered appearance suggests it was tumbled in a river or alluvial deposit.
Uses & applications
Used historically for stone tools due to its sharp fracture edges. Today, it is used as decorative stone, in lapidary work (jewelry), and as road ballast or construction aggregate.
Geological facts
Yellow jasper is a variety of chert colored by iron hydroxide (goethite) inclusions. It has been used by humans for hundreds of thousands of years to create scrapers and arrowheads.
Field identification & locations
Identified by its waxy texture, hardness (cannot be scratched by a steel knife), and smooth, curved conchoidal fractures. Commonly found in riverbeds and gravel pits.
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