sedimentary
Chert Breccia (Yellow Jasper)
Silicon Dioxide (SiO2) - Brecciated Chert
Hardness: 6.5-7 (Mohs scale); Color: Yellow-ochre with white/tan veinlets; Luster: Dull to waxy; Structure: Cryptocrystalline/Brecciated; Cleavage: None (Conchoidal fracture).
- Hardness
- 6
- Color
- Yellow-ochre with white/tan veinlets
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Yellow-ochre with white/tan veinlets; Luster: Dull to waxy; Structure: Cryptocrystalline/Brecciated; Cleavage: None (Conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich fluids in rock fractures or the lithification of silica-rich marine sediments. This specimen shows brecciation, where the original rock was shattered by geological forces/pressure and re-cemented by later mineral deposits.
Uses & applications
Used primarily for lapidary work, decorative landscaping, and as a collector's specimen. Historically used for stone tool making due to its hardness and sharp fracture edges.
Geological facts
Yellow jasper/chert gets its color from iron inclusions (goethite/limonite). Brecciated specimens are particularly prized by lapidaries because the 'shattered' pattern remains stable after polishing.
Field identification & locations
Identify in the field by its superior hardness (cannot be scratched by a steel knife), conchoidal fracture, and the visible network of internal fractures (brecciation). Frequently found in riverbeds or areas with localized tectonic activity.
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