sedimentary
Red Chert (Jasper)
Silicon Dioxide (SiO2)
Hardness: 6.5–7 (Mohs scale); Color: Red/orange (due to iron inclusions); Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.8
- Hardness
- 6
- Color
- Red/orange (due to iron inclusions)
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Red/orange (due to iron inclusions); Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.8
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria) or chemical precipitation from sea water. Often found in seafloor deposits that have been tectonically plates; ages can range from Precambrian to Cenozoic.
Uses & applications
Used historically for stone tools due to sharp edges; currently used for jewelry (lapidary), as a decorative garden stone, and as a collectible gemstone.
Geological facts
Red chert is often specifically called Jasper. It breaks with a conchoidal fracture, creating very sharp edges, which is why it was highly prized by indigenous peoples for arrowheads and scrapers.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial tills, and coastal outcrops.
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