Pictured: part of a deeply exceptional pearl containing versions of mineralization not found in the shell of Pinna species to which the pearl is attributed (source of this sample and its attribution to Pinna sp., from KCB Natural Pearls). There is just enough reasonably common prismatic shell material in the pearl to support the Pinna attribution. There is no trace of the nucleation 'agency'—to use Jameson's term explained elsewhere (see my &quot;Name the Origin of Pearls&quot;).