sedimentary
Banded Chert / Chalcedony
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs. Color: Blue-gray, brown, tan, and white. Luster: Waxy to vitreous. Structure: Microcrystalline/Cryptocrystalline quartz. Fracture: Conchoidal.
- Hardness
- 6
- Color
- Blue-gray, brown, tan, and white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs. Color: Blue-gray, brown, tan, and white. Luster: Waxy to vitreous. Structure: Microcrystalline/Cryptocrystalline quartz. Fracture: Conchoidal.
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Banding often occurs due to fluctuating mineral content during deposition.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for lapidary work, jewelry cabochons, and as a collector's specimen.
Geological facts
Banded chert has been used by humans for hundreds of thousands of years to create arrowheads and scrapers. Its ability to create spark when struck against steel also made it useful for early firearms.
Field identification & locations
Identify by its waxy texture, smooth conchoidal (shell-like) fractures, and its ability to scratch glass. Found frequently in riverbeds or within limestone formations.
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