sedimentary
Chert
Microcrystalline or cryptocrystalline quartz
AI-generated identification · may be incorrectHardness: 6.5-7 on Mohs scale. Color: Brown, tan, reddish, or yellowish (often due to iron oxide impurities). Luster: Waxy to dull. Crystal structure: Microcrystalline (trigonal). Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, reddish, or yellowish (often due to iron oxide impurities). Luster: Waxy to dull. Crystal structure: Microcrystalline (trigonal). Cleavage: None (conchoidal fracture).
Formation & geological history
Forms as a chemical sedimentary rock or a diagenetic replacement in other sedimentary rocks, often limestone or chalk. Composed of silica (quartz).
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Sometimes used as a low-grade aggregate or for striking sparks to start fires.
Geological facts
Chert can contain microfossils. Flint is a specific type of chert found in chalk or marly limestone.
Field identification & locations
Identified by its hard, dense nature, waxy luster, and conchoidal fracture. Often found as nodules in limestone or as layered deposits.
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