You should definitely take good quality photos of it, weigh it and make a post on here with the tag #silvergoldstackers include the photos ask the questions. Very, VERY knowledgeable people on here will help you. They'll tell you what is it, the purity and it's value. It sounds like a "sovereign" - possibly something like THIS

Don't trust some local gold place to give you a fair price. Most would low-ball you for certain - especially if they think you don't know what you've got.