sedimentary
Chert (specifically Yellow Jasper variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Yellow to brownish-yellow; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Yellow to brownish-yellow
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Yellow to brownish-yellow; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Used historically for stone tools (knapping) due to its sharp conchoidal fracture. Today used in lapidary work, jewelry, and as a collector's specimen.
Geological facts
Jasper is an opaque variety of silica that gets its distinctive yellow color from traces of iron hydroxide (Goethite). It has been used by ancient civilizations for seals and ornamentation for thousands of years.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces, its ability to scratch glass, and its waxy feel. Commonly found in riverbeds or eroded sedimentary outcrops.
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