Stone deposits can be found on every island. Clearing them will get you stones and XP. The bigger the stone deposit, the more stones you will get for clearing it.
As you explore you will find that there are stone deposits with blue rock. These deposits can be found on nearly every island. If you clear them you will get both stones and larimar.
Stone deposits will regenerate after you clear them. To learn more about when and where they regenerate, see the article Do Resources Regenerate on Home Island?
If you want to find out where you can find stone deposits with blue rock, check out the Archipelago Islands section.