sedimentary
Yellow Chert (River Stone/Pebble)
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale), Color: tan to honey-yellow, Luster: waxy to dull, Structure: cryptocrystalline (no visible grains), Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to honey-yellow, Luster: waxy to dull, Structure: cryptocrystalline (no visible grains), Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of microscopic silica-rich organisms (like radiolarians) or chemical precipitation in sedimentary basins. This specimen appears water-worn, indicating erosion and transport in a fluvial (river) environment.
Uses & applications
Historically used for stone tools; currently used as decorative gravel, in landscaping, or as a pocket stone for collectors. Occasionally used in jewelry if tumble-polished.
Geological facts
Chert and its variety, flint, were among the first materials used by early humans for tools because they fracture into razor-sharp edges. Yellow colors often come from iron oxide (limonite) inclusions.
Field identification & locations
Identify in the field by its smooth, waxy surface and conchoidal (shell-like) fractures. It will easily scratch glass and will not react with acid. Commonly found in riverbeds and limestone deposits.
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