James Risner wrote:
Saint Caleth wrote:
Orange Ioun Stone wrote:
Wearer adds one cantrip or orison (determined when the stone is created) to his list of spells known or spells prepared.
As far as I am reading, this might even allow an arcane spellcaster to use an orison or a divine spellcaster to use a cantrip.
It won't. This only allows you to add a spell you could already add to your spells known or memorized.
This will not add spells not already available to you.
I do not believe that is the case. The creator of the Ioun stone needs to know the spell to create the item. However, ioun stones are wondrous magic items and any character can use a wondrous item unless it specifies otherwise (per the CRB). Now, you have to be able to cast spells since it adds to your existing list only without granting you spell-casting ability(thus a fighter cannot use it but it does not mandate that it appear on your spell list)
There has been some discussion of this before but no definitive FAQ that I can recall.