Found this at the beach in sebastian, florida on the treasure coast. took it to a "we buy gold" place, they tell me its not gold based on an acid test on a stone. I have seen numerous pictures online with the same markings on both sides, and in a book my friend has, its exact based on the picture in the book. It weighs 20.2g and very clingy when dropped. no magnet reacts to it and the gold buyer tested with magnets also. what could it be?

