Because of variation in the composition of electrum, it was difficult to determine the exact worth of each coin. Widespread trading was hampered by this problem, as cautious foreign merchants offered poor rates on local electrum coin.
These difficulties were eliminated in 570 BC when pure silver coins were introduced. However, electrum currency remained common until approximately 350 BC. The simplest reason for this was that, because of the gold content, one 14.1 gram stater was worth as much as ten 14.1 gram silver pieces.Wow, historical basis for the 10 to 1 ratio of Silver to Gold coins in D&D. In my campaign world gold coins will really be made of electrum. Gold in its pure form is too valuable. Now players can't just melt down raw gold to make money (it happend once in a long ago game). Prices are more rational. Finally a coinage system that makes sense.
(ok bad pun)