Originally I posted this on the Dragonlance Forums, but I used to read both and so am posting on here just in case.
My memory is fuzzy, but the basics of the story are that a sorcerer/wizard is being held at a prison camp/fortress. He has to break out, but the guards have his necklace (or the other part to it) It's some sort of onyx type cylinder that goes over a pin (Somethign goes into it) and when it's put together it makes him very powerful, I believe at one point he uses it to summon cyclones/tornadoes.
AT first I thought it may be Dragonlance, but that doesn't sound like any books from the series I had read (this is over 7 years ago).