Makoto Koizumo of Koizumi Studio was inspired by river stones when he designed the Tetu Cast Iron Doorstop, which is made of Nambu cast iron (a material first used in the middle of the 17th century in northern Japan).

Above: The Tetu Door Stopper is 90 by 80 by 45mm; CA$65 at Mjolk. In the US, the Tetu Door Stopper is available through Emmo Home for $65.