Posted by Beth on April 29, 2015, 10:48 pm, in reply to "to jewellers"
In cut stones the shape is called sugar loaf cut.
I would use the same description i.e 'a sugar loaf shaped pearl' for the gem in HM's ring. The base appears to be flat as occurs in a button pearl - but we cannot be certain of that because it is hidden.
Because the shape is not round it could also be classified as a baroque pearl.