Naturally created by the Hearth Tree once every several hundred years,
About the size of a grapefruit, it is a brown sphere with light green veins running across the surface. The veins glow with a gentle light.
Can be used to create a Hearth Tree, a Guardian Wood, a Quickening, or many others.
The Seed Core may be the natural equivalent of the Magic Core. If this is true, the there may be many other types of Cores out there.