Skull crack (where to find it?)

[Edge the great]

I read here its found in iron horse mine, but ive been there for 5 hour yet i ahevtn found the boss that was mentioned there. So anyone else know where to find skull crack? thanks.

[Herthbul]

The boss only spawns on a Ranger quest. The other option is in the Spearhead Peaks on a boss called Hail Blackice (golem)