Congratulations. This pearl presents with features typically observed in it's class. Unlike other gemological pearl types, these bivalves are distinguished by having the two halves of the shell equally sized. In pearl reared species, normally the left valve is quite flat while the right is cupped. Being, homogenic in onset, the structure reflects the structure of the shell. It's largely calcareous, with minor aragonite. Purple colours almost always imply the thinnest pearl sacs, simply because the elegantly terminated crystals have no other alignment in the available space. While not highly spectacular on a world scale, it's a true gemstone nonetheless.
The surface is uniform, as is the colour. Despite the absence of higher gemological features expected from oriental or austral pearls, occidental pearls fulfill a desirable requirement for some discerning collectors. Edible clams as we know them have a small, but important niche market for their pearls. The purple colour, while not necessarily rare (I see it all the time) is considered uncommon, especially when gemologically described. Most pearls found in "steamers" tend to be inferior in so many ways to cultured pearls.
I agree with SteveM. The pairing of the object and it's host adds value. Finding a worthy natural pearl is not an everyday occurrence, thus retaining them, you may be among those who have. It's almost always my recommendation holding the item as a keepsake. It's an attractive pearl and a good story. The artist in me would be delighted to fashion this into something beautiful and special. Thank you for sharing it with us.