Heart of the Mountain

The Heart of the mountain is a new feature in the Dwarven Mines update. Which unlocks more levels by getting EXP for it will let you use more abilities and perks. It's a kind of skill tree that unlocks new pickaxe abilities. It requires 15 to use. Blocks of coal are abilities while the normal coal are perks. You can only use one ability at a time (they do not stack)