sedimentary
Banded Chert (Flint/Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Multi-colored bands (dark gray, black, brown, tan); Luster: Vitreous to waxy; Crystal Structure: Cryptocrystalline/Trigonal (detectable under high magnification); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Multi-colored bands (dark gray, black, brown, tan)
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Multi-colored bands (dark gray, black, brown, tan); Luster: Vitreous to waxy; Crystal Structure: Cryptocrystalline/Trigonal (detectable under high magnification); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in marine environments. Banding represents different mineral impurities or varying deposition rates over thousands to millions of years.
Uses & applications
Used historically for stone tools due to its sharp edges; modernly used as a decorative gemstone, in tumbling/lapidary hobbies, and as an industrial abrasive.
Geological facts
Banded chert is often associated with Banded Iron Formations (BIFs), some of which date back over 2 billion years and provide evidence of the 'Great Oxygenation Event' in Earth's history.
Field identification & locations
Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fractures where broken. It is harder than steel and will scratch glass. Look for it in riverbeds or coastal deposits. Found globally, with notable deposits in the Lake Superior region (USA) and Brazil.
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