Flint, close-up. This siliceous, sedimentary rock is here coloured by red or black iron oxides. This sample is from beds 1 to 2 metres thick that formed in the Oligocene (35 million years ago)) clays of the Malzieu basin. This stone was used during prehistoric times to make tools, and much later for gun flints. This specimen is part of the Geoscope geological park, located between Les Monts-Vert and Albaret-Sainte-Marie, central France.