Mega Ice

Mega Ice is the premier fire-melting ice in the Zelda universe, appearing in Spirit Tracks. An object of similar purpose also appears in Oracle of Seasons.

Oracle of Seasons
In Oracle of Seasons, enchanted ice are found in the Sword & Shield Maze and is used to freeze lava. It can be picked up with the Power Bracelet and thrown down holes. Though never given a name, it has a very similar role to the Mega Ice seen later on in the series in Spirit Tracks.

Spirit Tracks
In Spirit Tracks, Noko, an entrepreneurial Anouki from the Anouki Village, sets up shop at the Wellspring Station selling Mega Ice, after having trouble originally opening up for business in his home village. Mega Ice is used on many occasions, yet only once in a plot-required event - Link must transport the powerful ice from the Wellspring Station to the Goron Village so that the Gorons can reaccess sections of the village that had been quarantined off due to the virulent volcanic eruptions and fire geysers that had sprung up as a product of such magma outbursts in the area. The Mega Ice, as long as it is transported inside of the Snow Realm, will not melt, however, once Link ventures out into the Fire, Forest, or Ocean Realms, the 20 pieces of Mega Ice will begin to dwindle as a product of the increased light-intensity and higher temperatures in these other regions. To keep and preserve the fishstock on Papuchia Village, and in order to free up the last of the Goron homes in the Goron Village, Mega Ice must be transported beyond the Snow Realm. Since some of the Mega Ice-related sidequests require transporting the ice over long distances, the use of Warp Gates on the Spirit Tracks is highly advised in order to make it to the destination with the required amount of Mega Ice. The ice is also very fragile, so cautious, defensive engineering is a must when carrying the ice over long distances and through monster-infested regions. The Anouki at the Wellspring Station will sell the Mega Ice for 100 rupees the first time, and 50 rupees at any time after that, though on certain occasions, Link is able to comfortably barter the Anouki down to 25 rupees for the standard 20 pieces. However, Link can get the Mega Ice for free if he continues to badger the Anouki's prices down; regardless of price, the Anouki will offer to load the Mega Ice onto Link's train for free.

Trivia

 * Water Pots from The Wind Waker serve the same purpose as Mega Ice.