sedimentary
Brown Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 on the Mohs scale, Color: Brown to reddish-brown, Luster: Waxy to vitreous, Crystal structure: Microcrystalline/cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.60-2.65
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Physical properties
Hardness: 7 on the Mohs scale, Color: Brown to reddish-brown, Luster: Waxy to vitreous, Crystal structure: Microcrystalline/cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.60-2.65
Formation & geological history
Formed by the chemical precipitation of silica from seawater or the replacement of limestone by silica-rich solutions, often during the Paleozoic or Mesozoic eras.
Uses & applications
Historically used by ancient humans for making stone tools, arrowheads, and blades due to its conchoidal fracture. Today used in lapidary arts and as a specimen for collectors.
Geological facts
Chert is extremely durable and weather-resistant, which is why ancient stone tools made from it survive for millennia. Brown variations are often colored by iron oxide impurities.
Field identification & locations
Can be identified by its hardness (scratches glass easily), waxy luster, and sharp conchoidal edges when fractured. Commonly found embedded in limestone or chalk formations worldwide.
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