sedimentary
Chert (Common Opal/Chalcedony variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale). Color: Waxy white to translucent gray. Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Waxy white to translucent gray
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale). Color: Waxy white to translucent gray. Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Forms primarily as nodules or beds in sedimentary rocks through the precipitation of silica-rich fluids. In this region, it is often associated with the Lower Cretaceous or Tertiary sedimentary deposits of the Gulf Coastal Plain.
Uses & applications
Historically used for making stone tools (lithics). Modernly used as road aggregate, architectural stone, or for lapidary tumbling.
Geological facts
This specimen displays a distinct conchoidal (shell-like) fracture pattern characteristic of high-silica stones. The region near 33.0°N, 93.4°W (Southwest Arkansas) is famous for its diverse sedimentary silica variants, including novaculite and chert.
Field identification & locations
Identify by its waxy luster, ability to scratch glass, and sharp, curved edges when broken. It is extremely common in Arkansas gravels and riverbeds.
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