It was found in steamed clams? Quahog pearls are very sensitive to heat. They get mushy inside the skin which can crack like an egg.
It is a very dark one though it looks blue in the photo. Assuming it is not steamed, the value is still hard to guess.
I am "watching" one on Ebay. They want about 7k for it and it is not moving. It has been relisted numerous times, so far. I am sure it will never sell. they say it is 5 or so carats but don't give the mm dimensions! The price is well over 1k per carat, which I think is ridiculous, the seller just wants to list it, not sell it.
These pearls are scarce which is why the prices are high, but they are practically all listed as prices higher than good diamonds, and these pearls are very fragile. I would never put one in a ring, for instance. One guy who put up pix here had one from a grandparent and it was kept in a tiny bottle which was worn on a chain. Now that is one quahog pearl that is going to last unless the bottle breaks.
There are also some listings
here: Same problem, with prices. The ring has been up for years. Obviously, it is not priced to sell. The one that is not available on the above link did not sell; Kari puts a sold sign when it does, do I think the owner decided to keep it as a unique momento. I just checked and she does have some that sold, though she takes the price off, when it does. If you want to sell it, contact her. I just saw that the quahog ring she has up- 9carats It has been reduced to 5K- about $500 a carat. I still think that is way too high for such a fragile pearl.
That being said, there really isn't enough of a market to tell you a price that it will sell at. People has been showing us quahog pearls since the first year this site was open, and as far as I know not one of them has sold at the prices asked.
There is no replacement value because it is so unique, no amount of $$ will get you another one like it.