Heartstone

A heartstone is a fictional artifact common in dragon-related stories of high fantasy. It is a crystal of concentrated magic, and can be extracted from the heart of a slain dragon. It is believed that the heartstone is the source of a dragon's magic power, but this has never been proven definitively. Heartstones were considered a precious commodity in the Middle Ages, and were coveted for their wizard killing abilities. Generally the magnitude of a heartstone is directly related to the size of the dragon itself, though this is not always the case.