sedimentary

Chert (Yellow Jasper/Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Tan, yellow, or mustard brown due to iron oxides; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Tan, yellow, or mustard brown due to iron oxides
Luster: Waxy to dull

Identified June 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation within sedimentary layers. This piece appears to be a stream-tumbled river cobble, likely eroded from limestone or chalk beds.

Uses & applications

Used historically for stone tools and weapons due to its sharp edges; currently used for decorative landscaping, gravel, flintknapping crafts, and occasional lapidary work.

Geological facts

Chert is incredibly durable and chemically stable, which is why it often survives as rounded pebbles in riverbeds long after the surrounding rock has eroded away. Yellow varieties are often referred to as 'yellow jasper' by collectors.

Field identification & locations

Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fractures. It will easily scratch glass and will not react with acid. Commonly found in riverbeds, glacial tills, and sedimentary basins.

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