The Smooth Gem is an item from The Legend of Zelda: A Link Between Worlds. A magic gem that belongs to Oren, Queen of the Zoras, the gem is described as having an amazingly smooth texture.
Story[]
Spoiler warning: Plot or ending details follow.
When Link first arrives in the Zora's Domain, hoping to find a way to swim, he finds that the Shady Guy has stolen the Smooth Gem. Entering the domain, Link sees a bloated Oren, several times her normal size. Link travels to Kakariko Village in search of the gem, where he finds the Shady Guy. If Link sneaks up behind him. he will tell Link that he sold it to the Street Merchant, who will sell it to Link for 200 Rupees. The Smooth Gem can be retrieved without ever confronting the Shady Guy, however. When Link returns it to Oren, the restored Zora queen rewards him with the Zora's Flippers.
Spoiler warning: Spoilers end here.