sedimentary
Chert (Common Opal/Jasper variety)
Microcrystalline Quartz (SiO2) with hydration
Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, and translucent amber/yellow; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.7
- Hardness
- 6
- Color
- Tan, brown, and translucent amber/yellow
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, and translucent amber/yellow; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.7
Formation & geological history
Formed through the precipitation of silica-rich fluids within sedimentary rock cavities or by the replacement of organic material. This specimen likely formed in a volcanic or sedimentary environment where silica-rich groundwater deposited layers over millions of years.
Uses & applications
Used historically for stone tools due to its sharp edges; currently used for lapidary work, decorative landscaping, and as a collector's specimen.
Geological facts
Chert and its varieties like jasper and flint were the primary materials for prehistoric tools. The translucent amber section seen here is characteristic of common opal or high-silica chert often found in volcanic regions.
Field identification & locations
Identify by its conchoidal (shell-like) fracture, waxy feel, and its ability to scratch glass. It is commonly found in riverbeds, desert pavements, and exposed sedimentary layers throughout North America.
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