Mystery metal Jesus medal necklace

this is a platinum colored quarter sized Jesus medal on a solid sterling silver chain. the medal is marked 10k on the back but I am almost positive it is not gold but you can tell it is not a cheep medal it is very well made and the metal in the medal does not tarnish or rust? I really do not know the metal it is made of but the necklace is nice and easily be worn by a man or women just change the chain around is all it would take.