guild stone is known as nimbus and is only obtainable in game at 10am 16pm and 22pm server time in kaymo mountains its a guild pvp event and the guild who won the crystal quarry Battle i.e the ones who killed go-tor in kaymo mountains the previous night are the only guild who who can see and pick up the nimbus crystal. all other guild can obtain the crystal to do this u need to go to kaymo during the even times i have given above and kill someone from the winning guild who has picked up a numbus crystal.
1. Guild kills gotor the previous night to win crystal quarry extraction rights
2. Guild attends Nimus Crystal event (10am, 16pm, 22pm server time)
3. they extract nimbus crystal and attempt to deliver it safely
4. rival guilds try to stop them by killing them to obtain the crystal for there own guild
5. then rival guild tries to deliver it safely.
nimbus crystal when deliver gives your guild a guild stone and is also used by whoever obtains it to do 3 bath runs as the nimbus crystal when obtained restores hp over time.
hope this helps for more info check out your event tab under the guild section (crystal quarry battle and nimbus crystal)