From the beginning of recorded history, humanity has used all sorts of things as money. Salt, shells, beats, livestock - all had their day. But over time metals, particularly gold and silver, have emerged as the most widely used forms of money. This is not an accident. Precious metals have all the qualities that make money valuable and useful: scarcity, desirability, uniformity, durability, and malleability.
Even if people didn't want the metal as money, it still had value based on its other uses and relative scarcity.
In contrast, paper money has value only as long as enough people agree to take it in exchange for goods and services. But that makes its value completely subjective. Since it can be produced at will, and has no intrinsic value itself, the paper can become worthless if enough people lose faith in it.
— Peter Schiff; How an Economy Grows and Why It Crashes