Weirstones are magical items used by all Weir, and is their source of power, and is one of two essential items a Weir has, the other being his/her Weirbook. Each Weir is normally born with their respective Weirstone. In the case where one isn't, they will eventually die unless a Weirstone can be obtained. The Weir does not necessarily have to have the Weirstone of its associated Weir, so long as it has one. An example of this is Jackson Swift, who was born a Wizard, but was given a Warrior Weirstone to replace his missing one, saving his life. Magic powers are dependent on birth and the Weirstone received. Meaning, you are able to use the abilities of the Weir you were born into, and the abilities of the Weirstone you received. Jack can use both Wizard and Warrior powers. However, the natural abilities are very weak. The Weirstone provides the most magical power.