Heart Stone

Heart stone is the rarest gem known to all of Gilthanon. It can only be found in the deepest caverns of mountain ranges, and it's power is beyond measure. So named because it is the size of a human heart, this purple gem weighs unnaturally light. It is unbreakable by any means, physical, magical, or alchemical, and it is not meant to be ingested by men. It's purpose is mostly unknown, although some have tried to harness it's power, choking on the size of the stone before ever able to receive its magic.

One such instance lead to the creation of the fire demon ***. A nobleman who's expedition into the distant *** mountains brought back a Heart Stone, the prince spent years training himself to be able to withstand the ingestion of a stone such a size. He was able, through means of other stonecasters providing him with oxygen and relieving the pain, to swallow the stone, but its power engulfed him immediately, creating the fire demon. Fleeing back to its rightful home in Mt Oblivion, the demon, also named Oblivion, bled fire through the world, creating the fire scar still seen in the Third Age

(A Heart Stone is needed to bring clockwork to life, such in the case of Voldaroth and the black horse of Blugemburg.)