For the stone's properties to work, a spellcaster or someone proficient in the Arcana skill must perform a ritual which includes pressing the stone against the target's forehead for at least 1 minute. An unwilling target must be bound or otherwise restrained. Thereafter, the ioun stone becomes immaterial and orbits around the target's head at a distance of 1d3 feet. The person that performed the ritual can use an action to seize and stow the stone, ending its effect. Although the stone is visible, no other creature can grasp or affect it in any way. 

While this stone orbits the target's head, the creature can speak normally but cannot cast a spell requiring a Verbal component (or a command word, if casting a spell from a magic item). Sounds and words are distorted, and the spell fails. The caster, however, doesn't lose the spell slot.

If the target moves more than 500 feet from the person that performed the ritual, the effect ends and the stone reappears at the feet of that person. A DC 14 dispel magic or remove curse also ends the effect.

Notes: Debuff, Utility