You mean a Desert Slime? Aside from Legend of Zelda's fire or lightning ChuChu, your typical ooze or slime (for DnD and ChuChu's without special powerssuch as those from Twilight Princess) lives in moist environments such as sewers (for which most of their population exists and makes up a solid portion of), so a slime that needs no water at all would be quite unusual. My guess is that the silicon hardens enough during the cold nights for it to become a cube, while during the day the heat allows it to become as thin as a puddle.