sedimentary
Flint / Chert (Hag Stone)
Silicon Dioxide (SiO2)
Hardness of 7 on the Mohs scale, waxy to vitreous luster, conchoidal fracture, white to gray or brown color with concentric banding, cryptocrystalline quartz structure.
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Physical properties
Hardness of 7 on the Mohs scale, waxy to vitreous luster, conchoidal fracture, white to gray or brown color with concentric banding, cryptocrystalline quartz structure.
Formation & geological history
Formed in marine environments through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions during the Cretaceous period.
Uses & applications
Historically used for making stone tools and sparking fire; currently collected as a natural curiosity or talisman (hag stone).
Geological facts
Naturally occurring holes or rings in stones like this are often called hag stones, adder stones, or witch stones, and have historically been used in folklore as protective talismans.
Field identification & locations
Found commonly in chalk and limestone cliffs and beaches worldwide, particularly famous along the chalk coasts of England, France, and Denmark. Easily identified by its conchoidal fracture, smooth waterworn shape, and hardness.
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