Where Does Platinum Tone?

I found an earring that is heavy, gives me a tone in the gold range, but it is silver in color. Could it be Platinum, or White Gold? There are no markings on it, but it's weight leads me to believe it is a precious metal. I would have thought that it was silver, except my detector has never been wrong with silver. it is very close to the same size as a dime, but it is much heavier than a silver dime.

Any ideas as to what it is, and what is the best way to find out?