Estimated Value: 40,000 gp
The Regneration Ioun Stone is a pearly white spindle. You can use an action to toss this stone into the air, it orbits your head at a distance of 1d3 feet. While this pearly white spindle orbits your head, you regain 15 hit points at the end of each hour, provided that you have at least 1 hit point. Another creature can use an action to grasp or snare the stone to separate it from you, either by making a successful attack roll against AC 24 or a successful DC 24 Dexterity (Acrobatics) check. You can use an action to seize and stow the stone, ending its effect.
A stone has AC 24, 10 hit points, and resistance to all damage. It is considered to be an object that is being worn while it orbits your head.
Source: DMG p176