Ioun stone

Ioun stones, originally called Congenio's pebbles and later Ioun's stones, were magical stones that floated around a bearer's head and granted a range of 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.

Congenio's pebbles in the time of Netheril, −3462 DR to −3408 DR

Ioun stones after the Year of Wild Magic (1372 DR)

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.

It was rumored that Congenio Ioun himself had created another stone that had given him his great longevity; he lived almost a thousand years.

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.

In the time of Netheril, the gems and stones selected for enchantment were actually imperfect or flawed, with the exception of the perfect euhedral stone.

History
Congenio Ioun, an early arcanist of the Nether Age of Netheril, created the first ioun stones in the year 397 NY (−3462 DR). This was a previously unheard-of achievement: he was aged only 33 and this was the first magical item he had created, marking him as one of the greatest arcanists of his age. He initially called them Congenio's pebbles. Congenio worked under the (mistaken) assumption that only small or slender items—pebbles, small stones, pieces of cloth, daggers, and the like—could be enchanted to bear magic, and so he worked exclusively with small, semi-polished stones. He also adopted the self-imposed limitation of enchanting all stones of the same shape with the same spell, making them more consistent for buyers and eliminating confusion.

Congenio's pebbles soon became enormously popular with his fellow arcanists. Over the next 54 years, the anhedral, echinid, hexagonoid, spindle, pebble, star, and round stones were developed and introduced.

In 451 NY (−3408 DR), at the suggestion of a close friend, Congenio renamed his pebbles to the much more catchy Ioun's stones. Under this name, the cephaloid, cube, cylinder, decipton, dendroid, dodecahedron, ellipsoid, enneid, euhedral, hectoid, helicid, heptid, monoclinoid, nephroid, ovoid, octahedron, orthorhomboid, peg, pentahedron, prism, pyramid, rectangle, septahedron, sexahedron, tile, and tredyhedron stones were created and became widespread in Netheril.

Congenio himself created over thirty of these, including the prism that allowed one to see in the dark and another that granted its holder a temporarily raised level of experience and might. He was never seen without them orbiting his head. He lived an incredibly long life, almost a thousand years, and some wondered if one of his stones was responsible for his longevity. Congenio finally passed away in 1319 NY (−2540 DR), but for his creations his name lived on for millennia.

After his death, a number of other arcanists continued his work. These researchers made breakthroughs in Congenio's original design, by simply ignoring his consistent design and placing their own spells in whatever gem they had, no matter its shape. The stones became generally known as simply ioun stones around 1365 NY (c. −2494 DR). From this time on, the triclinid, tubule, decahedron, heptahedron, lozenge, rhomboid, rod, sphere, stelloid, and tetrapton were invented.

Notable collections
In the time of Netheril, Congenio's pebbles and Ioun's stones were in great demand among arcanists.

Larloch, the Shadow King, the arch-lich of Warlock's Crypt and a long-surviving arcanist of Netheril, 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, and he had multiples of some.

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.