Mithral

Mithral, also spelled mithril and known as truemetal among the dwarves, was a precious metal produced from ore found in the Underdark as well as mountain ranges in certain areas of Faerûn such as the Sword Coast North.

Description
Mithral ore appeared as a silver-and-black mineral in its natural form, and became a shining silvery-blue when it forged.

Mithral was produced through a process similar to that of steel-smelting.

Properties
Whenever a magical spell or spell-like ability struck an item forged from mithral the results were somewhat unpredictable. Seemingly half the time this occurred, the individual in possession of the mithral item became partially and temporarily protected from magic's harmful effects.

Uses
Items cast from mithral weighed only half as much as similar items forged from steel. Since pieces of armor made from this valuable metal were very light, they allowed the wearer to make better use of their natural agility and were less restrictive on spellcasting.

Rumors and legends
Among some bardic circles it was said that mithral combined with steel could create adamantine, but according to dwarves this claim was laughable. It was believed by some that dwarves simply did not wish to perform this difficult feat of metallurgy for anyone outside their race, unless they possessed an exceptionally good reason.