sedimentary
Chert (Yellow Jasper)
Silicon dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: tan to mustard yellow, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), SG: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to mustard yellow, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), SG: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine or groundwater environments. This specimen appears water-worn, likely from a river or glacial deposit.
Uses & applications
Historical use for stone tools (knapping) due to conchoidal fracture. Modern uses include landscaping, tumbling for collectors, and occasional use in jewelry as 'Jasper'.
Geological facts
Yellow chert gets its color from iron oxide impurities (limonite or goethite). It is extremely durable and can survive millions of years of transport in rivers.
Field identification & locations
Identify by its waxy surface, extreme hardness (it will scratch glass), and smooth, curved (conchoidal) breaks. Found globally in sedimentary basins.
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