You will be given a definition of a task first, then some input of the task.
You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: METALS 
Clue: Element No. 79, it's estimated that all of it ever mined would only make a cube about 50 feet across
Output:
gold