Chert (Common Opal/Jasper variety)

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.

Identified on: 5/8/2026

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