A Mithril ore deposit.
Mithril is a precious metal produced from ores found in mountain ranges in certain areas of Fantasia and in the Underdark. Mithril is produced with a process similar to that of steel smelting. Items made out of mithril weight half as much as similar items made of steel. Pieces of armor made mostly out of mithril are very light, therefore they allow the wearer to make better use of their natural agility and are less restrictive on the spellcasting.
Folktales[]
Among some bardic circles it is said that mithril combined with steel can create adamantine, but according to dwarves, this is laughable.