The STONSKIN.ITM is a undroppable item worn in the creature's ring/amulet/necklace slot - it can actually be placed anywhere on the creature. The item provides the wearer (typically a Mage) with an instantly cast Stoneskin spell.
It casts OHWI408.SPL upon the wearer while worn, and in most ways is the same as the usual Stoneskin spell used by players and most creatures in the game. It scales from 4 to 10 "skins" depending on the level of the creature equipped with the item. This item is provided to give the wearer some initial protection, without having to add a special script to do so.
The spell's duration is 60 turns (12-hours).
It has no other powers or abilities, however the item's effects do not add the characteristic grey colored hue over the creature, so there is no visual indication if the spell is active.