Mithril (aka True Silver) is a fantastic metal almost exclusively found in Elf crafted artifacts. Specifically, House Corundum has spent thousands of years jealously guarding the secrets of mining, alloying, and forging mithril.
Mithril is highly durable, holds an edge well against the most ludicrous stresses, and is as lightweight as aluminum. It is also an epic pain in the arse to work with even if you are a master of the art. Very few pure mithril weapons are known to exist today.
Modern Elven smiths prefer to alloy mithril with other more common materials, like aelum, bronze, or if absolutely necessary, iron. This process allows the creation of unenchanted armor with a fraction the weight its durability would suggest, with the bonus of near total corrosion resistance.