Uru
Uru, also called Star-Metal, is a metallic element unique to the star around around which the Nidavellir ringworld orbits.
Due to it's density, it is incredibly difficult to work with. The Star-Forge was created specifically to work the metal. Working Uru is a mark of high status in Dwarven society, and the regalia of the King of the Dwarves is forged from Uru.
Properties
Physical & Chemical Properties
Refined Uru is believed to be one of the strongest substances in the universe. The Dwarves claim is it is the densest mineral in existance, however this claim has not been verified by outside sources, due to the mineral's rarity and it's cultural importance to the Dwarves meaning that they rarely allow any to be taken off-world.
Uru is particularly good at channelling and containing magic, and grows stronger the more magic is placed in it. It is uniquely attuned to the natural magic of the Nine Realms and will absorb magic it is exposed to, even if not deliberably enchanted. It is unknown how it would react to magic from outside the Nine Realms. According to Asgardian myth, Mjolnir reacts to the presence of the Shi'ar goddess Phal'kon (also known as the Phoenix).
Geology & Geography
The element appears to be unique to the star around which the Nidavellir ringworld orbits. The heart of the star is a super-dense core of liquid Uru, which was originally mined using Dark Elf magic, and is now done using tools which were personally enchanted by Odin for the purpose.
Origin & Source
Attempts by Dwarven and Light Elf scholars to date the mineral deposits have failled, and some believe that the metal is from Ginnungagap, i.e. residue from before the big bang.
Uu
Type
Ore/Mineral
Color
Naturally grey, but can be chemically treated to create a golden sheen
Boiling / Condensation Point
5,505 °C (when unenchanted)
Melting / Freezing Point
196 °C (when unenchanted)
Captain America's Shield
Gungnir
Hofund
Infinity Gauntlet
Mjøllnir