sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dull brown to grey; Luster: Waxy to earthy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Dull brown to grey
- Luster
- Waxy to earthy
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Physical properties
Hardness: 7 on Mohs scale; Color: Dull brown to grey; Luster: Waxy to earthy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed in marine environments through the precipitation of silica from the remains of microscopic organisms like diatoms and radiolarians, or by chemical replacement of limestone.
Uses & applications
Historically used for making stone tools (flint knapping) due to its conchoidal fracture. Today used as road aggregate and in some decorative landscaping.
Geological facts
Chert is so hard it can scratch steel. Specimens containing ancient microscopic fossils can be billions of years old, providing evidence of early life on Earth.
Field identification & locations
Identify by its extreme hardness, waxy appearance on fresh breaks, and the way it chips into sharp edges like glass. Often found as nodules within limestone or as bedded layers.
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