What happens to the stone that faked cronus out?

Question

from the book mythology by edith hamilton

Answer 1

it technically got swallowed by him but in greek myth and history

it became the omphalos stone

it was supposed to mark the exact center of the earth.

Answer 2

Wiki

Once he had grown up, Zeus used a poison given to him by Gaia to force Cronus (Kronos or Kronus) to disgorge the contents of his stomach in reverse order:

FIRST -- the stone, which was set down at Pytho under the glens of Mount Parnassus to be a sign to mortal men.  The Delphic oracle is located at Delphi/Pytho being the place name. The site was considered the center of the earth, represented by a stone, the omphalos or navel.

Then the goat that nursed Zeus, and then his two brothers and three sisters.