Author's Note to The Hope, The Prince, and the Future
I have been asked what the round rock was that Gohan left to Trunks. Quite simply, it was the four star dragon ball. As you may recall, they turn to stone after the guardian dies, or in this case, the guardian's other half (piccolo).

Just to Clear that up for you!

SaiyanLover ((Vegeta, Goku, Trunks, Gohan, and Goten included)