Mabe pearls are cultivated from oysters and typically cut using the "blister" part only.  I choose this mabe because it was left in the shell which was choosen for it's rainbow flecks of color on top of blue.  Sterling silver wire was soldered to form the prongs and bail.  This pendant is about 2 inches tall.  This hangs from an 18 inch sterling silver chain with lobster clasp.  

Mabe Pearl and Sterling Silver