sedimentary
Chert (Jasper)
Silicon Dioxide (SiO2) with impurities
Hardness: 6.5-7 (Mohs); Color: Red, brown, yellow, white; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Red, brown, yellow, white
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Red, brown, yellow, white; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed by the precipitation of silica from groundwater or oceanic fluids within sedimentary rocks. Often found in nodules or bedded deposits dating from various geological eras.
Uses & applications
Historical use for stone tools/arrowheads; currently used for landscaping, lapidary work (jewelry), and as a decorative stone.
Geological facts
Red chert is often called Jasper. Its microcrystalline structure makes it very brittle but sharp when broken, which is why it was prized by prehistoric humans for tool-making.
Field identification & locations
Identify by its hardness (it will scratch glass), smooth waxy feel, and conchoidal (shell-like) fracture patterns. Found globally in limestone and chalk beds.
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