The staff room is a cave where you can access by going to the left of the teleporter. To get there you need to go to the bridge and swim left to the end of the river near where the Upgrade Pickaxe area is. Once you touch the cave you'll be taken to the Staff Room. The Staff Room is the only place you can get Garnet. There are 5 garnet per server, 4 on the ground, 1 on the wall and they do not respawn. To make more garnet spawn, everyone must leave the staff room to make a new staff room server.