A geocoin is a metal or wooden token minted in similar fashion to a medallion, token coin, military challenge coin or wooden nickel, for use in geocaching, specifically as form of a calling card.[1]
Many of these are made to be trackable on various websites to be able to show the movement around the world[2] and visitors to be able to leave comments when they find the coin. Each coin has a unique tracking ID, which can also be used when logging it to a designated website.[3][4]
A geocoin typically has a diameter of 1.5 inches (38 mm) to 2 inches (51 mm) and a thickness between 0.098 inches (2.5 mm) and 0.16 inches (4 mm). Coins with the size of 1 inch (25 mm) are called microcoins, because they fit into microcaches (e.g. film canister). The smallest geocoins with a diameter of 0.5 inches (13 mm) are called nanocoins, and have been sold since 2009. If the diameter is larger than 3 inches (76 mm) the geocoin is called macrocoin, and contains the saying of "that’s not a coin, it’s an anchor".