sedimentary
Chert (Jasper variety)
Microcrystalline quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Reddish-orange with cream mottling; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Reddish-orange with cream mottling
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Reddish-orange with cream mottling; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids, often in marine or limestone environments.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for lapidary work, jewelry (cabochons), and decorative landscaping.
Geological facts
Because it breaks with a conchoidal (shell-like) fracture, it was one of the primary materials used by prehistoric humans to create arrowheads and scrapers.
Field identification & locations
Identify by its waxy texture, inability to be scratched by a steel knife, and smooth, curved fracture surfaces. Found worldwide in nodules within limestone or as bedded deposits.
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