Altmyr is a rock that can be shaped and formed into weapons like metal. It is incredibly lightweight but extremely strong, and it channels magic well. It is believed that it formed when the sorcerers of the world worked to stop the fire mountain that was constantly erupting to destroy farms and other lands in Berk and periodically in Phelin. The sorcerers’ magic solidified the molten rock, and the magic itself became a part of the rock. It is believed that this magic within the stone is what makes the Altmyr so useful for channeling magic, and gives it the ability to be used as weapons and armor.