The current 1 oz. American Gold Eagle has a legal tender face value of $50 meaning it is legally equal in purchasing power to a $50 Federal Resrve Note. It is obvious that you would not go out and buy something for $50 with the gold coin. This is Gresham’s Law at work, the government does not want people to use gold in every day transactions. If the government valued the face value to the current price, instead of having a $50 face value, they might actually circulate and compete with FRN, which of course will never happen.