They answered you on the other thread where you first posted your message. Did you look after posting? People post on finding these quahog pearls frequently here, although they aren't common.
Was the clam cooked before you found the pearl? You didn't answer that question and most people don't eat raw clams. If it wasn't cooked, it might have some value.
As an aspiring appraiser, I can tell you that it's worth what someone else is willing to pay for it. Because it doesn't have a market, and is, as Catilin says, an oddity, you can find out its value by auctioning it off, say, on eBay. When you have something that doesn't have a defined market, you can have trouble finding a buyer.
By all means, please take and post a photograph and people will give you their thoughts. Asking about it without giving specific details such as size, color and a photo, is pointless. There was a lot of information in the first thread you posted on. You can also search for Quahog in the search box above.