sedimentary
Chert (specifically Yellow Jasper variety)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 Mohs scale; Color: Opaque yellow to mustard-brown due to iron oxide inclusions; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
- Hardness
- 6
- Color
- Opaque yellow to mustard-brown due to iron oxide inclusions
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs scale; Color: Opaque yellow to mustard-brown due to iron oxide inclusions; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical precipitation of silica in groundwater. Often occurs as nodules in limestone or as bedded deposits. Geological age varies widely from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Currently used for lapidary work, decorative landscaping, bead making in jewelry, and as a collector's specimen.
Geological facts
Yellow jasper was historically used by ancient civilizations as a protective stone. Because it breaks with a conchoidal (shell-like) fracture, it creates edges sharper than a surgical scalpel, which is why it was a primary material for arrowheads and scrapers.
Field identification & locations
Identify in the field by its waxy luster and smooth, curved fracture surfaces. It cannot be scratched by a steel knife. Common in diverse locations like the Western USA, Brazil, and India. Collectors look for uniform color or unique 'landscape' patterns within the stone.
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