sedimentary
Chert (Jasper/Limonitic Chert)
Silicon dioxide (SiO2)
Hardness: 6.5-7. Color: Yellow-brown, tan, ochre. Luster: Waxy to dull. Crystal structure: Microcrystalline/Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Yellow-brown, tan, ochre
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7. Color: Yellow-brown, tan, ochre. Luster: Waxy to dull. Crystal structure: Microcrystalline/Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Chemical sedimentary rock formed by the precipitation of silica-rich fluids in marine environments or through the replacement of limestone. The yellow-brown color is caused by iron oxide (limonite) impurities.
Uses & applications
Historically used for stone tools and weapons due to sharp edges when fractured. Today used in construction aggregate, landscaping, and as lapidary material for jewelry (Jasper).
Geological facts
Chert is so hard it can strike sparks from steel, a property that was used in flintlock firearms. This specific color variety is often referred to as 'yellow jasper' in the gem trade.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife), conchoidal (shell-like) fracture patterns, and smooth, waxy texture. Commonly found in riverbeds and sedimentary basins.
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