Ice Rock

An Ice Rock (Japanese: こおりでおおわれたいわ Ice-covered rock) is an ice-covered rock that enables Eevee to evolve into Glaceon.

Not to be confused with Ice Stone or Icy Rock.

An Ice Rock in the anime

In the core series games, if an Eevee is leveled up in an area containing an Ice Rock, it will evolve into Glaceon. Even if Eevee meets other evolutionary conditions when leveled up, the Ice Rock will still cause it to evolve into Glaceon rather than Espeon, Umbreon, or Sylveon.

In the core series games

In Sinnoh, an Ice Rock is located a short way south from Snowpoint City on Route 217. It is located in an area where the blizzard is very rough, on the easternmost part of the route. It actually appears that the rock is located in the backyard of a house that is near a female Skier. It is surrounded by long grass.
In Unova, an Ice Rock is located in the basement of Twist Mountain, just west of Icirrus City. It is located on the lowest floor, past an NPC who gives the player Fossils of previous regions. Eevee must be leveled up in the room with the Ice Rock in order to evolve into Glaceon; it will not evolve into Glaceon by leveling up anywhere else in Twist Mountain.
In Kalos, an Ice Rock is located deep within Frost Cavern. Surf is required to access it.
In Hoenn^ORAS, an Ice Rock is located on the lowest floor of Shoal Cave, accessible only when the tide is low.
In Alola, an Ice Rock is located inside the cave in Mount Lanakila.
In Hisui, an Ice Rock is located in a subterranean cave in the Bonechill Wastes in the Alabaster Islands.

There is no Ice Rock in Kanto, Johto, or Galar. In Pokémon HeartGold and SoulSilver, this means that Eevee cannot evolve into Glaceon at all—Glaceon can only be obtained by trading with Pokémon Diamond, Pearl, and Platinum.

Starting in Generation VIII, Eevee can also evolve into Glaceon using a Ice Stone even without an Ice Rock.

Appearance

Sinnoh	Unova	Kalos	Hoenn	Alola

In spin-off games

Pokémon Mystery Dungeon series

Due to the Ice Rock's absence in Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness, Eevee evolves into Glaceon through the use of the Frozen Rock, and the same method in Gates to Infinity.

Pokémon Conquest

In Pokémon Conquest, Eevee evolves into Glaceon when it is deployed in Nixtorm while it has an Attack stat of 91 or higher.

In the anime

An Ice Rock appeared in a flashback in A Full Course Tag Battle!, where it was revealed that May had visited it in a cave near Snowpoint City in order to evolve her Eevee. Unlike the games, where an Eevee must be leveled up but can be anywhere in the area housing the Ice Rock, May's Eevee promptly evolved into a Glaceon upon touching the Ice Rock, much like an Evolution stone.