The Marretaela amulet is an enchanted object, worn by Thorin Ulfarsson in Books 1-3. It depicts a hammer, which is the official symbol of the mining clan Marretaela.
The amulet cannot be used to cast magical attacks. It is for defense only, and protects the wearer against harm. Dwarf weaponry and amulets are in high demand throughout the kingdom of Durn.