After the statue is completed, the pearl should be at the foot of the statue. Put a mater builder on it & he/she will bring it to the waterfall to 'reshape' & 'finish' it & then when that person is done doing that, have a master builder pick it up again (the pearl will still be at the waterfall) & he'll bring it to the research lab. Then take the tribal chief the the research lab & drop her on the pearl. She will then take it to the clam & 'trade' & bring the green key that was originally in the clam to the door.