Dark Ore

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

Link can purchase ten pieces of Dark Ore and take them to Linebeck III in the Trading Post. Doing so will reward the young hero with a Force Gem from Linebeck to gain access to Lost at Sea Station in the Ocean Realm. However, to get it transferred quickly to Linebeck III, Link must travel through the cave on the right side of the Fire Realm and fight a large Rocktite and its small children.

Trivia
The Dark Ore does not disspear when it is in the snow realm, leading most to believe that the ore actually melts due to the sun's heat, rather than the sun's light.