In Argentina, in el Valle de la Luna, we have a place with a lot of big natural stone spheres. They are bigger than the sphere in the picture, so perhaps it has a different geological origin. <a href="http://commons.wikimedia.org/wiki/File:Valle_de_ichigualasto,_cancha_de_bochas.jpg" rel="nofollow">http://commons.wikimedia.org/wiki/File:Valle_de_ichigualasto...</a><p>More info about natural stone spheres: <a href="http://en.wikipedia.org/wiki/Stone_ball#Natural" rel="nofollow">http://en.wikipedia.org/wiki/Stone_ball#Natural</a><p>Some pages with photos of similar places:<p><a href="http://101lugaresincreibles.com/2010/10/cinco-sitios-con-rocas-esfericas-que-parecen-talladas.html" rel="nofollow">http://101lugaresincreibles.com/2010/10/cinco-sitios-con-roc...</a><p><a href="http://www.cesarlizano.name/sibowak/esferas_de_piedra_costa_rica_htm/esferas_de%20Piedra_en_el_mundo.htm" rel="nofollow">http://www.cesarlizano.name/sibowak/esferas_de_piedra_costa_...</a>