Common Stone is an item in the “Unused” category (Key Items).
In-game descriptions
| Sun / Moon · Ultra Sun / Ultra Moon · Let’s Go, Pikachu! / Let’s Go, Eevee! · Sword / Shield | A perfectly normal stone that might appear to be valuable to some. It’s all in the eye of the beholder. |
|---|
Where to find it
Not placed on the atlas maps (so far: Red/Blue and Generation 3).
Sources : PokeAPI (items, item_flavor_text, machines) · atlas · pokeemerald species_info.h