sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brownish-grey with waxy luster, Structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-grey with waxy luster, Structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Specific gravity: 2.65
Formation & geological history
Formed in marine environments through the precipitation of silica from seawater or the accumulation of siliceous skeletal remains (like diatoms or radiolarians) within sedimentary layers.
Uses & applications
Historically used for making stone tools and weaponry; currently used in construction aggregate, road surfacing, and as a decorative landscaping stone.
Geological facts
Chert is so durable that it can survive long-distance transport in rivers and glaciers. It sparks when struck against steel, which made it essential for early firearms like flintlocks.
Field identification & locations
Identify by its smooth, waxy surface and characteristic curved (conchoidal) breaks. Often found as nodules in limestone or as water-worn pebbles in riverbeds.
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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