Red Ice

From Zelda Wiki.org

Red Ice is found in Ocarina of Time after Link becomes an adult. It is found in Zora's Domain, the Ice Cavern, and Ganon's Castle and vaguely resembles a pale red version of Nayru's Love.

When Adult Link first enters the now-frozen Zora's Domain, most of the Zoras are gone and King Zora is trapped within Red Ice. The only way it can be melted is with Blue Fire, which can be bought for 300 Rupees at some shops (Empty Bottle required), or found in the Ice Cavern and Ganon's Castle. Many objects in the Ice Cavern are encased in Red Ice and require Link to melt it so that he can gain access to them.