I have a gold coin wich is sealed in plastic case an has little black spec inthe case?

Does the speck look organic or does it look artifishiul???? if it looks liek print or somthing put there by the companie thin it should be fine! but you could have a scam in your hands too. that black dot could be from someone who has opened the case and resealed it!!! hmmmmmm idk

You have a piece of foreign matter in the case and it made that black mark on the coin. You did not state which gold coin, for some cases can be opened. Gold is a pretty hardy metal, even sea water will not eat it. It is best to take it to a couple of coin dealers and get their opinions. Since I can't see it that us the best I can do.