sedimentary
Chert (Common Opal/Agate inclusion)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7.0 (Mohs). Color: Olive green to tan with translucent chalcedony/agate patches. Luster: Waxy to dull. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Olive green to tan with translucent chalcedony/agate patches
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7.0 (Mohs). Color: Olive green to tan with translucent chalcedony/agate patches. Luster: Waxy to dull. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the chemical precipitation of silica-rich fluids in sedimentary environments or as a replacement mineral in limestone/volcanic ash. This specimen shows significant water-rounded smoothing, likely from a river or beach environment.
Uses & applications
Historically used for stone tools (flintknapping); currently used for decorative pebbles, tumbling, and lapidary art. High-quality translucent pieces may be used in jewelry.
Geological facts
Chert is essentially the same mineral as jasper and flint, distinguished primarily by color and origin. Large deposits are often the result of microscopic sea organisms (like diatoms or radiolarians) accumulating on the ocean floor.
Field identification & locations
Identified by its waxy texture, conchoidal (shell-like) fracture patterns when broken, and inability to be scratched by a steel knife. Commonly found in riverbeds and gravel pits.