Ioun stone

Ioun stones, originally called Congenio's pebbles, were magical stones that granted enhancements or powers to a creature.

Description
They were small, crystalline stones, coming in a wide range of colors and shapes that determined their powers.

Powers
Ioun stones hovered permanently in the air.

When one acquired a stone and wished to receive its benefits, they had to first hold it for a brief time and then release it. Thereafter, when functioning, the ioun stone floated in a circular pattern around the bearer's head, at a distance of 1–3 ft (30–91 cm). They could only bestow their benefit on an owner when within this range. Two stones of the same type would repel each other. Another person could try to catch or net the stone to steal it, or break it. The bearer could freely grab and pocket a stone, such as when going to sleep, to keep it safe, but they could no longer receive its benefits.

The stones granted various benefits based on their color, as listed below. When drained of power, a stone became a dull grey, but it still possessed the characteristic floating power.

As with other items that could store magical energy, the pale lavender ellipsoid, lavender-and-green ellipsoid, and vibrant-purple prism could store spellfire. In turn, they could also be drained by a spellfire wielder.

Creation
Ioun stones could only be created by a veteran spellcaster well versed in the crafting of wondrous magical items.

Only certain types of gemstone could be transformed into an ioun stone through application of the appropriate and generally secret spells. These gems were known collectively as "the nine secrets", though there were at least ten. These were amethyst, chrysoberyl, chrysoprase, greenstone, hematite (though this was rarely known to even powerful wizards), iol (also known as iolite or cordierite, and the most effective of the gems), Laeral's tears (most little known and rarest of the gems), obsidian (the most well known), onyx, and sardonyx.

History
Congenio Ioun, an arcanist of Netheril, created the first ioun stones.

Notable collections
Larloch, the Shadow King, arch-lich of Warlock's Crypt, possessed over two dozen ioun stones, which orbited his skull at all times, giving him a wide variety of powers, protections, and enhancements. Some were much more powerful than their regular versions.

The Wyvern Crown of Cormyr was inlaid with ten ioun stones on the tips of its spikes. None of the stones could be removed from the Crown without destroying them, not without a wish spell on each stone.

A ring of a dozen ioun stones was occasionally sighted hovering above the River Vesper in the Vast from the 1350s DR on. The stones avoided efforts to grab them, and by 1370 DR, no one with a net, the ability to fly, or a magical means of catching one was lucky enough to spot the ring. A tale told in riverside taverns claimed that anyone who could grab one of the ioun stones could keep it, but was also compelled by a geas to perform some dangerous task, with a different task for each stone.