Black Oyster Pearl 1 – Burial-stained black right valve of European Flat Oyster shell (Ostrea edulis Linnaeus) showing a “pearl” attached to the inner nacreous surface by a short stalk near to the adductor muscle scar. Shell found on Rhossili Beach, Gower, South Wales.
Jessica's Nature Blog 
I have found two different Oyster shells with black pearls much like your picture from the Chesapeake Bay in Maryland and was wondering how rare are they?
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I am really not at all sure, Larry. I have not heard about attached black pearls on oyster shells anywhere else apart from yourself. However, it could simply be that this is a fairly common phenomenon that has been often observed but not recorded.
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