sedimentary

Chert (Yellow Jasper/Flint)

Silicon Dioxide (SiO2)

Hardness: 7.0 (Mohs scale); Color: Yellow to tan with iron staining; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65.

Hardness: 7
Color: Yellow to tan with iron staining
Luster: Waxy to dull

Identified March 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as a sedimentary rock through the accumulation of silica-rich microfossils or chemical precipitation within limestone or dolostone layers. This water-worn specimen likely originated from Paleozoic or Mesozoic strata and was tumbled in a riverbed.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges. Currently used as an abrasive, in decorative landscaping, or as a lapidary material for tumbling and cabochons.

Geological facts

Chert is so durable that it often survives long after its original host rock has eroded away. Yellow varieties are frequently called 'Yellow Jasper' when opaque and are colored by goethite or limonite inclusions.

Field identification & locations

Identify by its waxy feel, hardness (will scratch glass), and lack of visible grains. Common in river gravels and outcrops throughout North America. Collectors look for smooth, colorful nodules free of internal fractures.

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