Dark Ore

Dark Ore is an item in.

Location
Found only in the Dark Ore Mine in the Fire Realm, the ore costs 200 Rupees for ten pieces. The ore is said to shine in the dark but begins to disappear (or melt, depending on who Link asks) at a fast rate when exposed to sunlight, and as such, Link must quickly transport it to its destination before it completely disappears.

Uses
Link can purchase ten pieces of Dark Ore and take them to Linebeck III in the Trading Post. If Link can successfully bring at least five of these pieces to Linebeck, he will reward the young hero with a Force Gem, which will energize new tracks in the Ocean Realm allowing him to gain access to Lost at Sea Station. However, to get it transferred quickly to Linebeck III, Link must travel through the cave on the east side of the Fire Realm and fight a large Rocktite and its small children. If Link's train is attacked more than once, he will not be able to bring a sufficient amount of ores to Linebeck (i.e. less than five). If Link still takes these few ores to Linebeck, he will reward Link's efforts with 100 Rupees. This, however, does not compensate for the cost of the wasted ores.

Afterwards, if Link brings five or more ores to Linebeck once again, he will reward Link with a treasure (usually one of 500 Rupee worth).

Trivia

 * Bringing the Dark Ore to Linebeck III for a Force Gem (or treasure) is the only use for them throughout the game. Later deliveries, however, are rewarded with treasures as rare as the Alchemy Stone.
 * Linebeck's use for Dark Ore is never explained in the game.