We are made of sturdier materials than we give ourselves credit for. The human body can withstand a staggering force before our bones give way to the stresses. So too is it for the bones of animals, especially those of Ashenfall. Here, the magic seeps into the marrow and strengthens the bone to be sturdier than before.
When used as tools, refined into weapons, these bones can be made to break stone and release metal ore from its prison.