sedimentary
Yellow Chert (Chert / Jasper)
Silicon Dioxide (SiO2 / Microcrystalline Quartz)
Hardness: 6.5-7 on Mohs scale; Color: Tan to yellow-brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 6
- Color
- Tan to yellow-brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan to yellow-brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich fluids in sedimentary environments, often as nodules in limestone or as bedded deposits. This specimen appears water-worn, likely from a stream or river bed.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp conchoidal fracture. Used today as decorative gravel, in lapidary work, and for casual mineral collecting.
Geological facts
Chert is so durable that it resists weathering better than surrounding rocks. Yellow-colored cherts often get their hue from small amounts of iron oxide (goethite) mixed within the silica.
Field identification & locations
Identify in the field by its smoothness, hardness (it will scratch glass), and its tendency to break with curved, shell-like surfaces. Found in riverbeds and limestone outcrops worldwide.
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