sedimentary
Chert (Jasper/Flint variety)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Brown, tan, reddish; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Brown, tan, reddish
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, tan, reddish; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids within sedimentary rock layers, often occurring as nodules or beds.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges; currently used for decorative stone, landscaping, and lapidary art including cabochons.
Geological facts
Chert is so hard it can scratch steel and was used by ancient humans to create sparks for fire-starting. Jasper is an opaque variety specifically valued for its aesthetic patterns.
Field identification & locations
Identify by its waxy appearance and shell-like (conchoidal) fracture pattern. Commonly found in limestone beds, riverbeds, and gravel deposits globally.
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