Navel Rock (Japanese: へそのいわNavel Rock) is an island between Floe and Chrono Islands in the Sevii Islands, accessible in FireRed and LeafGreen, and Emerald. It can only be accessed after downloading the MysticTicket through Mystery Gift and sailing there by talking to the sailor in front of the Seagallop Ferries in FireRed and LeafGreen, or by boarding the S.S. Tidal in Emerald. Unlike the other Sevii Islands, and like Birth Island, Navel Rock does not appear on the Town Map by default.
A colored background means that the Pokémon can be found in this location in the specified game. A white background with a colored letter means that the Pokémon cannot be found here.
Trivia
The island shares similarities with Navel Island in the Orange Islands; not only do they both have the word "navel" in their names, they are also home to an extremely tall mountain.
Interestingly, the island's music in Emerald is identical to Pokémon FireRed and LeafGreen's music, sharing 3 of the same tracks as the FireRed and LeafGreen soundtracks.
There is a glitch location, Sevii Isle 8, that has blank map data for the location where Navel Rock is. This may be due to undeleted beta programming, as there are what appear to be sealed-up cave entrances, or may just be data for the outside of Navel Rock, as it is usually entered through the ferry.