Here are all the locations of the Summon Materia's for Final Fantasy VII.
Talk to the Chocobo at the front of the farm and reply "Waaark".
At the Junon coast after saving Pricilla.
On the boat after beating Jenova-BIRTH.
Lying on the floor in the Chocobo Jockey waiting room.
In the wreckage of the Gongaga reactor.
Defeat the Lost Number enemy inside the Shinra mansion safe.
Defeat everyone in the Pagoda in Wutai.
Walk to the second area in the Sleeping Forest and it will be floating around. Wait in the spot
where it is first seen, then tap O button to take it. If you don't catch it at first you can follow it until you do.
This Summon uses Lightning, Ice, and Fire Magic all at once, so don't use it against an emey who absorbs any of those Elements.
After the snowboarding sequence, find the hot spring and touch it. Then find the area where you leave markers
and keep to a straight path. Find the hut there and enter. Leave through the downward facing door. Go right, find the cave
and talk to the person inside. Defeat her and the materia will fall from the sky.
Defeat the red dragon at the Cetra shrine.
Defeat the Ultimate Weapon a few times until it dies. A crate will remain. Go to the jelly
object on top of the mountain. Its at the end.
After Geas cliff; just pick it up.
Found while collecting the Huge Materia at Mount Condor. After defeating the enemies the man
sends you out to check on the condor egg. The Materia is up there, shining and bouncing.
On the wreckage in the Gelinka.
Collect the four Huge Materia. You must also have the other two Bahamut Materias. Store
them in the Observatory, then look closely at the Blue Huge Materia.
Knights Of The Round
Found on the island only on the final disc. It is unmarked at the top right of
the map, and requires a Gold Chocobo to reach it.