sedimentary
Yellow Chert or Jasper
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Yellow, mustard, or buff; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Yellow, mustard, or buff
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Yellow, mustard, or buff; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich marine organisms or from volcanic ash precipitates in sedimentary environments. Can be billions of years old or from recent geological eras.
Uses & applications
Used historically for stone tools and arrowheads; currently used in jewelry (cabochons), as an abrasive, and by crystal collectors.
Geological facts
Chert is one of the oldest materials used by humans to make tools due to its sharp edges and hardness. Yellow varieties are often colored by the presence of iron oxides like goethite.
Field identification & locations
Identify by its waxy texture, inability to be scratched by a steel knife, and smooth, curved (conchoidal) fracture patterns. Frequently found in riverbeds and limestone deposits.
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