From Bulbapedia, the community-driven Pokémon encyclopedia.
Silver Rock Isle (Japanese: 銀岩島 Gingan Isle) is an anime-exclusive location in Johto, and one of the four main islands in the Whirl Islands archipelago. It has a strong connection to the Silver Wing and to the Legendary Pokémon Lugia.
It first appeared at the end of Plant It Now... Diglett Later, when Ash and his friends took a ferry from Red Rock Isle to the island. In Hi Ho Silver... Away!, the group visited the island's only known town, Kasado City, and met Jenaro and Ariene.
It is home to one of the hardest and purest substances in the world—silver rock stone, and its main attraction is the jewelry made from the stone.
An underwater cave system connects Silver Rock Isle to Ogi Isle.
Silver Rock Isle is the home of Top Coordinator Robert.