THE MYSTERIOUS STONE SPHERES OF COSTA RICA

The spheres range in size from a few centimetres to over 2 metres (6.6 ft) in diameter, and weigh up to 15 tons.[4] Most are sculpted from gabbro,[4] the coarse-grained equivalent of basalt. There are a dozen or so made from shell-rich limestone, and another dozen made from a sandstone.

They appear to have been made by hammering natural boulders with other rocks, then polishing with sand. The degree of finishing and precision of working varies considerably. The gabbro came from sites in the hills, several kilometres away from where the finished spheres are found, though some unfinished spheres remain in the hills.[citation needed] They are used for decoration.