sedimentary
Chert (Yellow Jasper/Flint)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Yellow-brown with white/tan patination; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Yellow-brown with white/tan patination
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellow-brown with white/tan patination; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed as chemical precipitates from silica-rich fluids in sedimentary environments, often replacing carbonate material. This specimen shows a weathered outer layer (cortex).
Uses & applications
Historical use for stone tools (arrowheads); currently used as landscape stone, in gravel, and by lapidary hobbyists for tumbling or cabochons.
Geological facts
Chert is so hard it can scratch steel. When struck against iron or pyrite, it produces sparks, which led to its extensive historical use as flint for starting fires and in firearms.
Field identification & locations
Look for the characteristic 'shell-like' conchoidal fracture patterns on broken edges. It is often found as nodules in limestone or as smooth river pebbles.
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