Red Ice

Red Ice is found in Ocarina of Time as Adult Link in Zora's Domain, the Ice Cavern, and Ganon's Castle. Link's first encounter with the substance is upon his return to Zora's Domain seven years into the future: King Zora, as a product of the freezing of Zora's Domain, is trapped cold within a block of this Red Ice. Blue Fire is the only remedy for relinquishing King Zora from his icy red cage, and for dealing with any and all Red Ice found throughout the rest of Link's quest; Blue Fire can be bought for 300 Rupees at some shops and bazaars (Empty Bottle required), or found in the Ice Cavern and Ganon's Castle. Many objects in the Ice Cavern are encased in Red Ice, such as wooden chests and rupees, which must be melted down in order to access.

Trivia

 * This impregnable ice vaguely resembles a pale red version of Nayru's Love.
 * Red Ice may be based off of the crystallization of supersaturated sodium acetate solutions, also known as hot ice.