Platinum

Platinum is a rare silvery-white metal sometimes used as a currency in the Realms. It's value is generally greater than gold and, like gold, it's resistant to oxidation.

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