The stone spheres (or stone balls) of Costa Rica are an assortment of over three hundred petrospheres in Costa Rica, located on the Diquis Delta and on Isla del Caño. Known locally as Las Bolas, they are also called The Diquis Spheres. These are the best-known stone sculptures of the Isthmo-Colombian area.
The spheres range in size from a few centimetres to over 2 metres (6.6 ft) in diameter, and weigh up to 16 short tons (15 t). Most are sculpted from gabbro, the coarse-grained equivalent of basalt. There are a dozen or so made from shell-rich limestone, and another dozen made from a sandstone.
Numerous myths surround the stones, such as they came from Atlantis, or that they were made as such by nature. Some local legends state that the native inhabitants had access to a potion able to soften the rock. Research led by Joseph Davidovits of the Geopolymer Institute in France has been offered in support of this hypothesis, but it is not supported by geological or archaeological evidence. (No one has been able to demonstrate that gabbro, the material from which most of the balls are sculpted, can be worked this way.)
It has been claimed that the spheres are perfect, or very near perfect in roundness, although some spheres are known to vary by 5 centimetres (2.0 in) in diameter. Also the stones have been damaged and eroded over the years, and so it is impossible to know exactly their original shape. A review of the way that the stones were measured by Lothrop reveals that claims of precision are due to misinterpretations of the methods used in their measurement. Although Lothrop published tables of ball diameters with figures to three decimal places, these figures were actually averages of measurements taken with tapes that were nowhere near that precise.