sedimentary

Chert (Yellow Jasper variant)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Tan, yellow, off-white; Luster: Dull to waxy; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Tan, yellow, off-white
Luster: Dull to waxy

Identified March 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or sponges) or chemical precipitation in sedimentary basins; it can be found in strata ranging from Precambrian to Cenozoic ages.

Uses & applications

Commonly used as construction aggregate or road base; historically used for stone tools (lithics) due to its sharp conchoidal fracture. Collectors value high-quality colored variants (Jasper) for lapidary work and tumbled stones.

Geological facts

Chert is so hard it can scratch steel and was used by prehistoric humans to make arrowheads and knives; when struck against steel, it can produce sparks, leading to its historical use in flintlock firearms.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) breakage patterns and its inability to be scratched by a steel knife. It is frequently found in limestone or chalk beds globally. Collectors should look for unique banding or bright colors.

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