sedimentary
Chert (Green)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Muted green/grey; Luster: Waxy to vitreous when wet; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Muted green/grey
- Luster
- Waxy to vitreous when wet
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Physical properties
Hardness: 6.5-7 Mohs; Color: Muted green/grey; Luster: Waxy to vitreous when wet; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed as a chemical precipitate from silica-rich fluids or from the accumulation of siliceous microfossils (like radiolaria) on the ocean floor, subsequently compacted and hardened during diagenesis.
Uses & applications
Historically used for making stone tools; currently used as road aggregate, in landscaping, and as a decorative collector's item.
Geological facts
Chert is a broad category that includes flint and jasper. Green varieties often get their color from trace amounts of chlorite or other silicate minerals.
Field identification & locations
Identify by its waxy texture and sharp, shell-like (conchoidal) edges when broken. It will scratch glass and does not react with acid.
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