Gorak claws are common drops by Goraks. Using a set of claws with a Pestle and mortar creates Gorak claw powder, which is the secondary ingredient used in making the Magic essence potion.
Gorak claws are sometimes gathered by players with little money who cannot afford to make potions with expensive ingredients such as herbs. Because both ingredients of the magic essence potion are free, it is one of the few potions that can be made without gathering herbs. However, because Goraks are so powerful, and prayer cannot be used against them, this method is rarely used.
For an exhaustive list of all known sources for this item, see here