sedimentary
Yellow Chert or Jasper
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Honey yellow, brown, tan; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Honey yellow, brown, tan
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Honey yellow, brown, tan; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (radiolaria or diatoms) on the ocean floor or through the chemical replacement of limestone by silica-rich groundwater. Often found as rounded river or beach cobbles.
Uses & applications
Used historically for stone tools (arrowheads due to conchoidal fracture); currently used as aquarium decor, lapidary material for tumbling, and landscaping.
Geological facts
Chert and Jasper are essentially the same mineral; Chert is usually more translucent while Jasper is opaque. This specimen shows significant rounding from water erosion, suggesting it was found in a river or coastal environment.
Field identification & locations
Identify in the field by its waxy texture when wet, extreme hardness (it will scratch glass), and its tendency to break into sharp, curved surfaces. Commonly found in gravel pits and along shorelines globally.
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