sedimentary
Chert / Flint Nodule
Cryptocrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, waxy to vitreous luster, conchoidal fracture with sharp edges, colors range from white, grey, yellowish-brown to black, microcrystalline structure with no visible crystal faces.
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Physical properties
Hardness of 7 on the Mohs scale, waxy to vitreous luster, conchoidal fracture with sharp edges, colors range from white, grey, yellowish-brown to black, microcrystalline structure with no visible crystal faces.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions or the replacement of limestone/chalk by silica-rich fluids in marine environments, often occurring as nodules within sedimentary rock layers.
Uses & applications
Historically used for making stone tools, arrowheads, and spark generation in firearms. Modern uses include abrasives and ornamental lapidary work.
Geological facts
Ancient humans prized chert and flint for their ability to fracture with extremely sharp edges, known as conchoidal fracture, making them ideal for cutting and hunting tools during the Stone Age.
Field identification & locations
Can be identified in the field by its hard conchoidal fracture, waxy luster, and occurrence as nodules within limestone or chalk formations. Collectors often find them weathering out of sedimentary cliffs or riverbeds.
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