The Wilderness skeleton mine has the most number of coal rocks in all of Gielinor. It is located in the level 9 Wilderness, south of the Dark Warrior Fortress. It is nearby to a similar low level Wilderness mine that is known as the Wilderness steel mine.
The skeleton mine can be a viable alternative to the often crowded Mining Guild coal, especially when a Charged Dragonstone Amulets is used by the player in order to teleport to Edgeville bank and quickly empty their inventory.