Band of Rumination

Band of Rumination is a very good ring for casters of any kind.

In the RPG
Rings of this type are carved from a single chuck of raw amethyst, capped with a black pearl in a truesilver setting. In darkness, the ring glows with a faint purple hue.

Source
This item dropped from Warchief Rend Blackhand in Upper Blackrock Spire.