Where is the gem stone on islend six in Pokemon fire red vershion?

There is no "Island Six" in Pokemon Fire Red version. The game only has four islands:

* One Island: The starting island with Pallet Town, Viridian Forest, and Pewter City.

* Two Island: The island with the route to the Safari Zone and the cities of Celadon City, Lavender Town, and Saffron City.

* Three Island: The island with the routes leading to the Power Plant, the Sevii Islands, and the cities of Fuchsia City, Cinnabar Island, and Victory Road.

* Four Island: The island with the Kanto region's final route and the Indigo Plateau.

If you are looking for a specific gem stone, you'll need to specify the location on one of these islands.