Polished Stone is a Rare Fortnite Wrap. Polished Stone was available via the Battle Pass during Season 21 and could be unlocked on Page 9 and costs 4 Battle Stars.
How-to Get the Polished Stone Wrap
Polished Stone is part of Season 21. If that season is still currently in the game, you can obtain this item by purchasing and/or leveling up your Battle Pass.