I Need An Evil Object

I have reached the point in my new novel where I need an evil object. It contains the power to destroy the world. What is that object?

Here's a few bits and pieces about the book- It concerns a 25-year old black wizard who is forced to buckle down and assume guardianship over a vast hoard of magical and evil objects gathered and stored for the purpose of keeping them out of the hands of evil-doers. His adversary is his two-years younger female sibling who has become a corrupted, demented megalomaniac who wants to kill him and gain trouble of all these objects. She arranged the murder of their father, and the young man was nearly killed  the same attack. He has since hooked up with a not quite 21-year old white witch-druidess with a complex heritage. Together, with a little band of black and white practitioners they have to protect the magical treasure hoard, and especially this one particular object that rests in a vault deep beneath the earth underneath the 1600's family homestead. The sister can only gain access to the treasure and this object upon the death of the current guardian, her brother.

The brother is a potter, like his father before him and so forth back in time. The white witch/druidess wotks in her family's nursery.

What is the simple, unassuming object that contains all the evil energy that when it falls into the wrong hands has the power to destroy the world?

I need an evil object...but it has to be an ordinary object...and a back story, if possible, although I could probably think of a story...any suggestions?