sedimentary
Red Chert (Jasper)
Silicon Dioxide (SiO2) with iron oxide inclusions
Hardness: 6.5-7 (Mohs scale); Color: Brick red to brownish-red; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brick red to brownish-red
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brick red to brownish-red; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the recrystallization of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. The red color comes from iron oxide (hematite) impurities integrated during deposition.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp conchoidal fracture. Modernly used for lapidary work, jewelry (cabochons), and as landscaping stone.
Geological facts
Jasper has been used as a gemstone since antiquity and is mentioned in the Bible. Large deposits in the Pilbara region of Australia are over 3 billion years old.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), conchoidal (shell-like) fracture patterns, and lack of visible grains. Commonly found in riverbeds, glacial tills, and as nodules in limestone or seafloor deposits.
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