sedimentary
Chert (Nodule)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: Grey, tan, or brown with concentric banding, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Grey, tan, or brown with concentric banding, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed by the precipitation of silica in sedimentary rock layers, often replacing limestone or forming as nodules during diagenesis in marine environments.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction as aggregate or by collectors for its unique banding patterns.
Geological facts
Chert nodules are extremely durable and often survive the weathering of surrounding limestone. They were the primary material for prehistoric flintknapping.
Field identification & locations
Identify by its 'waxy' texture and curved, glass-like (conchoidal) fractures. Found commonly in limestone outcrops and riverbeds.
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