From Guild Wars 2 Wiki
Jotun Runestones are ancient stones from the time before the jotun fell to civil war and their current primitive state. They hold the jotun's ancient writings and are valued by the Durmand Priory, though viewed as little more than currency by modern jotun. The runestones can either be traded for more items, or given directly to Albin to gain renown in the heart quest.“
Albin Chronicler is very interested in these.
— In-game description