He is talking about the ruby & sapphaire gemstones that will power the machine he is working on and let you trade from Pokemon Ruby & Pokemon Sapphaire 7 the ruby and sapphaire
Gemstone? Where'd you hear about that? PokeFakes.Org or something.
It is likely to be one of those Bogus items. it has no purpose and intrigues the mind of naive Pokemon trainers.
give it to celio
You give it to Celio
he is in one island in the hospital.
Give it to Celio on one island.
You get a map from Celio, on one island.
Get the crystals on 1,2,3,4,5,6,7 islands and bring to Celio.
If you mean Celio, his in one island pokemon center.
in the dotted hole on island 6
find the ruby and give it to celio.
you can catch mewtwo at cerulean cave
Give it to celio in 1 island
go to one island and talk to celio