Ioun stone

Ioun stones, originally called Congenio's pebbles, are magical items often manufactured by spellcasters.

Description
When functioning, ioun stones float in a circular pattern around their bearer's head, and grant various benefits based on their color. Two stones of the same type will repel each other. When drained of power, a stone becomes a dull grey, but still possesses the characteristic floating.

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