Queen Mab’s crown, was created by Grimsen. It was magically and wondrously wrought so that it passes only from one blood relation to another in an unbroken line. With the crown passes the oaths of all those sworn to it, although her subjects gather at each new coronation to renew their fealty. The authority still rests in the crown.
This makes it difficult to take the throne of Elfhame by force. A condition of the crown was that there must be two royal children when a coronation takes place, one to crown and one to be crowned. Only when there are less than two descendants of Mab's line will the crown be broken.
It is described as a simple golden crown crafted to form oak leaves.