I have an ingot, just like a piece of silver in the movie. I don't know if it is copper or gold. Who can tell me how to distinguish it?

Diamond weighs 0.31ct, color F, clarity vs1,18K platinum claim 3.15g, with a GIA certificate. How much does it cost? The cutting is excellent, and the symmetry is also Excellent. Diamonds are 8 arrows and 8 hearts.

Now there are many fakes on the market, I accidentally buy it wrong if I accidentally