sedimentary
Chert (Iron-stained)
Microcrystalline Silica (SiO2)
Hardness: 7 (Mohs scale), Color: Rusty orange to brown, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, Cleavage: None
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Physical properties
Hardness: 7 (Mohs scale), Color: Rusty orange to brown, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, Cleavage: None
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. The rusty color indicates the presence of iron oxide (limonite or hematite).
Uses & applications
Historically used for making stone tools (flintknapping) due to its sharp edges; modern uses include construction aggregate and decorative landscaping stone.
Geological facts
Chert is so hard it can easily scratch glass or steel. Its conchoidal fracture pattern is the same as that of obsidian and glass.
Field identification & locations
Identify by its waxy texture, extreme hardness, and lack of visible grains. Often found as nodules in limestone or as rounded river cobbles.
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