Glalie's stone Quest
You start at Vermi's Library and you need to interact with the top right book shelve
The book tells us that Glalilite is now 4 fragments that we need to find
There are 4 locations, each one with one fragment
Ice Path (Johto) / Seafoam Island (Kanto) / Lake Acuity (Sinnoh) / The last one is the remain ice stone at Shoal Cave (Hoenn)
Fragment n°1 : Ice Path
You need to go to Ice path B1F and interact with the big ice rock under the northernmost hole.
Just wait and don't move for 2 minutes (Poketime not real time) and click again to obtain the 1st fragment !
Fragment n°2 : Seafoam Island
Enter Seafoam Island by the left entrance (from fuschia). Take the 1st ladder in your way. You must arrived there
Go South and to the right, take the last stairs (don't take the ladders) go up and interact with the second big ice rock
You just need a Pokemon in your team with the move Flash to obtain the 2nd fragment.
Fragment n°3 : Lake Acuity
Go to Lake Acuity (near Snowpoint city) and interact with the second rock on the lake.
You will need to surf around the lake and stay close to the border (follow the blue line between lake and border). You will also have to turn around the lake anticlockwise so from the south of the lake to the right etc..
You have to start under the rock, close to the border and finish your turn there. If you succeed, you will have a dialogue : you can get your 3rd fragment from the rock !
(Hint : Refresh every 3 - 4 steps to be sure you're on the border)
Fragment n°4 : Shoal Cave
Go to the Shoal Cave (low tide)
03:00 - 09:00 / 15:00 - 21:00 (Pokétime)
You'll need a low IV glalie and put it in slot 6. I don't know what is the maximum IV needed. Mine was under 60 IV.
You get the 4th fragment when you have the right glalie. Now, you have to find a rock's expert ...
Get the Glalie Mega Stone
Go to the Pewter's Museum and speak to the scientist to the right. You just need 6 ice pokemon in your team.