You can get to the vault through The Old Mine which is accessable through the Arwic Mines dungeon. Once you're outside of the Old Mine you can start running toward the Serac Vault at 75.9S 29E.

Make sure to buff before entering the vault. It's suggested to go in as a group to avoid deaths. There's no exit portal so be prepare to fight till they all drop. Once the place is clear proceed forward and avoid the first cooridor and continue heading East into the next cooridor. Enter the cooridor which curves toward South. Keep heading forward (South) and follow the curvive till you come upon a jump down the pit. Jump down and continue heading forward which will take you to a plateform at the end. Hope over to the plateform and head West (left). Continue till you come upon another plateform. Make the jump and continue jumping for the plateform that's to the furthest to the West. While facing West make a right turn and continue heading forward. When at the door the lever on the right is the one that opens this door and the one to the left is your target. Use the [ or ] to select the lever to pull the levers. Once lever is pulled hurry back the other way and keep following the path till you're at a big pit. Turn left a little and jump on the plateform where the wooden door is. The door should be open and make a run for it before it closes. The stone spawns behind this set of doors across from the bridge. The spawn rate for the stone is about 30 seconds. Enjoy. Note: If you can't target the lever head the opposite direction and follow it till you come upon a big pit. There are two wooden planks sticking out from the wall to the right where you'll see a lever. Pull this and head back to the door.

Major Shivering Stone Value: 5000 5 Burden Units Use this stone on an Empyrean weapon or on a piece of Shadow Armor.