sedimentary
Brown Chert
Cryptocrystalline Silica (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs), Color: Brown/Grey, Luster: Waxy to Dull, Crystal structure: Microcrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Brown/Grey, Luster: Waxy to Dull, Crystal structure: Microcrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed in marine environments through the precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (like diatoms or radiolarians). It forms within sedimentary rock layers like limestone or chalk.
Uses & applications
Historically used for stone tools and arrowheads. Currently used as an aggregate in construction, road surfacing, and as a polishing media. Fine specimens are used for folk art and flint knapping.
Geological facts
Chert has been used by humans for over 2 million years because it breaks with a razor-sharp conchoidal fracture. Some varieties contain well-preserved microfossils and can vary greatly in color based on mineral impurities.
Field identification & locations
Identify by its waxy luster, extreme hardness (it scratches glass), and curved glass-like fractures. It is commonly found as nodules or layers within limestone beds or as smoothed river stones.
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