Easy first go up to mt ember on one island then go to where there are two rockets battle them and then go through the hole find your way you find it
if u mean the ruby it is on one island after you beat the Pokemon league and have the national pokedex.
1 island 6 island
you find the ruby in the cave right next to mount ember on island 1. to get the sapphire gem you have get the pass from celio to go to island 4567 and it is on island 6
Head north on Island 1, and keep heading north until you see two rockets. You must have defeated the Elite 4 and gotten the National Dex.
use cut. ;)
at mt ember after fighting the rocket grunts and going in mt ember
FireRed. If Ruby, Sapphire, and emerald you must have Ruby and Sapphire gem and give it to celio in one island
mining it
after u battle th first gym leadr
The gem is on six island not seven island and its inside a cave called dotted hole.
After getting the nationaldex, go to one island and talk to celio. He will tell you to find the ruby and sapphire gem and give you the rainbow pass which give access to the 4, 5, 6 and 7 islands. If he does not give the pass, first find the ruby gem in Mt. Ember and give it to him. Then, he will surely give you the pass.
After you have obtained and restored the Sapphire gem, you now are given the ability to trade with trainers from the Hoenn region. Mind you these need to be your real life friends, and they can give you all the Pokemon from Ruby, Sapphire, and Emerald.