Thank you for sharing your photo of the stingray "pearl".
These types of objects are often called Mustika Pearls or Bezoar Stones and occur in many plants and animals. If you do a search on the internet for them, you will find sites majoring in these types of unusual things. They are sometimes used for mystical purposes or collected as items of curiosity.
They can form in the digestive systems or heads of a large variety of animals and occur in various colors and sizes.
These types of objects are rare and highly prized especially among the oriental cultures.
I suggest you contact some of the sites that major in them for possible sale.
