Types of rocks of the pre-precolumbian spheres

They were made mainly from three types of rocks:

Gabros, Monzogabros, Granodiorites 

These types of rocks belong to the Puerto Nuevo Formation and surface at the South Pacific region of Costa Rica, in sites like Puerto Nuevo, Grisera, Coyolar, Disciplina, Changuenita, Canchén, Zapote, Yan and Boruca.

The time of emplacement of these rocks occurred between 18 to17 million years ago, and 15 to 11 million years ago.

These gabbros, monzogabbros and granodiorites are intrusive igneous rocks. They result from the solidification of magma at important depths within the earth’s crust, so they cool down slowly; minerals have time to grow, and create large crystals observable to the naked eye.

Limestones

This is another type of rock of those used to create stone spheres. Those observed belong to the Fila de Cal Formation. The outcrops of these rocks spread along Fila Costeña, from Ciudad Neily to Ciudad Cortés, and in other regions such as Damas, Providencia, Cuesta de Cal, and Fila Cajón. 

Deposition of these rocks occurred during the Middle-Upper Eocene (some 48 to 34 million years ago), during a period with a decrease in volcanic activity that allowed the oceans to receive less sediment; consequently the water was clear, turbulent, with normal light and salinity rates. This situation favored coral reefs to thrive in the coasts’ shallow areas.