Some pawn shops, jewelry stores or gold refineries etc will do an analysis of the gold in an item/piece for free, if you take your item/piece to them and ask them to tell you how much they are likely to pay for it.
You may go to a store, shop or refinery near you if there are any, and you may also want to do this too with those that will do the analysis for you why you wait too. Alternatively you can also use a jewelry appraiser who can also do the analysis for you too, even though this is a paid service, the choice is yours.
You need such an analysis (test) to know the actual gold content (that is, 14K, 18K etc) of any item or piece.
Gold nuggets usually have up to 20.5K to 22K of gold content/purity, this may vary in some other countries or locations.
The gold content of an item can be determined by carrying out a gold analysis or test on the item.