Mithril

Mithril is a type of armour that can be bought, created and worn by Free-to-Players, as well as members of Runescape. Mithril, or 'Mith' for short, is a blue color, darker than the Runite blue.

Mithril is better than Bronze, Iron, Steel, and Black armour.
Mithril ore can also be mined to make Mithril bars.
You must be mining level 55 to mine mithril. 

Mithril bars sell for 1k each.

5 coal ore and 1 mithril ore are needed to make a Mithril bar via a furnace or superheat.

If you are using the blast furnace in Keldagrim, half the amount of coal is needed. Mithril armour requires 20 defense to wear, and full armour costs around 8k. You can buy mithril armour from the Grand Exchange or other players. Mithril armour is used for low level players and high level members in the Warriors guild.