Petrosphere

Several classes of petrospheres exist, such as the stone spheres of Costa Rica; painted pebbles from Scotland; stone charms from Scotland; sandstone balls from such sites as Traprain Law; the Carved Stone Balls, which are mainly from Scotland, although they have also been found in Cumbria England, and Ireland; and carved stone shot for cannons and trebuchets. The word comes from the Greek petros and sphaira. Naturally-formed stone balls, i.e. cannonball concretions and megaspherulites, have been at times misidentified as petrospheres. For example, fringe archaeologists and advocates of prehistoric extraterrestrial visitors have repeatedly argued that the stone balls, which range in diameter from 0.61 to 3.35 meters, found around Cerro Piedras Bola in the Sierra de Ameca, between Ahualulco de Mercado and Ameca, in Jalisco, Mexico, are petrospheres. However, these natural stone balls are megaspherulites that have been released by erosion from a 20 to 30 million year old ash flow tuff, which originally enclosed them and in which they formed.