I Want Mussel(s)!!! (long live Grace Jones!)

Ok, so here's the deal ... my dude and I decide to visit Short Hills Mall in New Jersey last night to pick up some things and afterward we were hungry so we decided to eat at a spot within the mall called Legal Sea Foods. Ever been? Well, I'd been once before a few years ago in Boston, so I knew it was good stuff and felt comfy with a return. My dude ordered the Legal's New England Clam Chowder, the Fried Fisherman's Platter and we shared the Classic Caesar Salad. I ordered the Nutty Atlantic Salmon for an entree and for a shared appetizer, I ordered the Mussels ... they came out ... the waiter commented on how fragrant they were just as I was thinking it and I quickly cosigned him verbally with a "yessssss they do smell goooood". The garlic scent was heavy and I loved it! He exited and my dude and I toasted. He began to taste the soup and commented how creamy it was, better than another place we went to oddly enough in Boston, but not the same trip in which I first dined at Legal Sea Foods. Ok, so that was his first scoop of soup and comment ... my turn. So, I looked over the bowl and picked out the first one. It was large, wide open and ready to go with a big chunk of chopped garlic right on the edge of it's opening. It had first bite written all over it. I released it from it's shell and gave it a go. Just about two chews in I got a hard crack on my tooth, I thought to myself, "Arrrooo?", like Scooby Doo. My dude was watching my face and caught the look because he was intently awaiting my first reaction as I did his. So, I took one more tousle and chew and hit it again, quickly followed by me doing that food isolation thing we do in our mouths so I could better feel it. At first feel it surely wasn't jagged like a possible shell piece or debris. Simultaneously, I could tell my face was confusing because I was in turn getting a confused face from across the table. I grabbed a napkin and as discreetly as possible emptied the clinker into the napkin to reveal a larger than pea-sized, rounded, black, smooth, but irregularly shaped around the edges mass. I said to myself before I passed it over the tabletop, "Is this what I think???? -- It can't be". I passed it and said something close to, "Look at this. Is. This. uhhhh... what is it?". My dude was just as dumbfounded as me, like are we seeing what we think we are? We both decided, let's call our waiter over and give him a look. A second later he passed by and we gave him the nod, he made a swift turn to us and asked what we needed. I told him it was within the first mussel I tried. He took a look and his first guess was that it looked like a "tiny mussel". I immediately said, nooo ... look at it. Then I thought to myself, not that a mussel can't be smooth, but this was smooth and had a different sheen to it and color as well. The waiter said he'd go check with the chef. Ok, I said and he returned with the verdict ... the chef said in his opinion he agreed with me. :-) Looks as though, it may actually be a natural black pearl. WHAAAA!?? So, look, it may be a rock for all I know ... until I take it to an appraiser. What I can say is it was within the mussel where a pearl would be and If you've never heard of a pearl from a mussel, give a quick search online. I've become a bit more acquainted myself in the last day. Here's the pic .... albeit flash heavy due to the low light and the low quality of a cell phone flick ...

What do you think it is???

I guess I need to find an appraiser, huh?