sedimentary
Chert (Iron-stained)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: tan, orange, reddish-brown (from iron oxide staining), Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, orange, reddish-brown (from iron oxide staining), Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of organisms or chemical precipitation from silica-rich groundwater within sedimentary host rocks like limestone or dolomite.
Uses & applications
Historically used for making stone tools (flintknapping). Today used as road aggregate, architectural stone, and occasionally in lapidary work for cabochons.
Geological facts
Chert is extremely durable and weather-resistant. In its dark gray to black form, it is commonly known as flint. The orange-brown staining in this specimen is likely due to the oxidation of iron minerals like goethite or hematite within or on the stone.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth conchoidal fracture, and it often has a 'ring' when struck. Commonly found in stream beds or within limestone outcrops.
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