Electrum

Electrum is a natural alloy of gold and silver and to a minor degree of copper. The color depends on the mixing proportion of silver or gold.

Worth
Most coins in Faerûn work off of the silver and gold standard, with copper pieces (cp) being worth 1/100th of a gold piece (gp), and Silver pieces (sp) being worth 1/10 of a GP, electrum coins are worth 5gp, and platinum coins are worth 10gp.

Conversion
Simplified: 1000cp = 100sp = 10gp = 2ep = 1pp