Where do you get the special gem in Pokemon FireRed?

You're likely thinking of the Shiny Stone, which is used to evolve certain Pokemon in Pokemon FireRed. Here's where you can find it:

* Route 12: There's a hidden cave on Route 12, accessible by going through the tall grass. Inside, you'll find the Shiny Stone along with a few trainers to battle.

The Shiny Stone is essential for evolving:

* Togetic to Togekiss

* Roselia to Roserade

* Minccino to Cinccino

Note: You can also obtain the Shiny Stone via the Game Corner in Celadon City by trading in enough coins. However, this is a very expensive way to get it.