Coal is an ore that can be acquired using the Mining skill. It requires level 30 to mine. Coal can be combined with other ores in a furnace to create different types of bars.

Coal needed Ore needed Bar created
2 Iron ore Steel bar
4 1 Mithril ore Mithril bar
6 Adamant ore Adamant bar
8 Runite ore Rune bar

. It is used in many quests.

Once a player has 60 Mining they can asses the Mining Guild in Falador, This is by far the largest deposit of coal ore along with 4 Mithril ore respawns.