sedimentary
Flint
SiO2 (Cryptocrystalline Quartz)
Hardness of 7 on the Mohs scale; color ranges from dark grey, black, brown to white; waxy or vitreous luster; microcrystalline or cryptocrystalline structure; no cleavage, exhibits conchoidal fracture; specific gravity of around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; color ranges from dark grey, black, brown to white; waxy or vitreous luster; microcrystalline or cryptocrystalline structure; no cleavage, exhibits conchoidal fracture; specific gravity of around 2.60 to 2.65.
Formation & geological history
Formed by the replacement of calcium carbonate by silica in chalk or limestone beds during the Cretaceous period through diagenesis.
Uses & applications
Historically used for making stone tools, weapons, and fire-starting (strike-a-light). Modern uses include abrasives and decorative landscaping.
Geological facts
Flint was crucial for human survival during the Stone Age due to its ability to break with sharp edges (conchoidal fracture). It is a variety of chert specifically found in chalk formations.
Field identification & locations
Easily identified in the field by its dark color, smooth weathered cortex, conchoidal fracture, and extreme hardness. Commonly found along chalk cliffs and beaches, such as the white cliffs of Dover.
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