The heartstone is a stone given to Saba by Mercy. Lugh, Emmi, and Saba's mother had given it to Mercy. It is usually cold unless if the wearer's heart's desire is near, then it is warm.
The heartstone a rosy pink stone. It is smooth and oval shaped, like a bird's egg. It is threaded on a leather thong, and is the size of Saba's thumb.