sedimentary

Chert (Common Opal/Jasper transition)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Tan, cream, yellow-orange; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65

Hardness: 6
Color: Tan, cream, yellow-orange
Luster: Waxy to vitreous

Identified May 31, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Tan, cream, yellow-orange; Luster: Waxy to vitreous; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65

Formation & geological history

Formed through the accumulation of silica-rich fluids or biological remains (like radiolarians) that precipitate in sedimentary basins. These specimens appear to be secondary silica replacements in a volcanic or sedimentary environment.

Uses & applications

Used primarily for lapidary work (cabochons), flintknapping (arrowheads), and as decorative landscaping or collector specimens. Historically used for making fire and tools.

Geological facts

Chert is so durable that it is often found as rounded pebbles in riverbeds far from its source. High-grade translucent varieties are often classified by collectors as 'Common Opal' or 'Chalcedony'.

Field identification & locations

Identify by its waxy texture and sharp, shell-like (conchoidal) fractures. It will scratch glass but cannot be scratched by a steel knife. Common in limestone regions and volcanic ash beds.