The Clam Key is the fifteenth puzzle in Virtual Villagers 3.
You cannot do this puzzle unless you've solved the statue puzzle first.
As soon as the statue is finished you will be able to see a white pearl appear.
Drop a Master Builder over the pearl and they will take it to the waterfall, the pearl will turn blue.
The pearl will be taken to the lab by the Master Builder once you drop them on the blue pearl. The Master Builder will take it to the lab and polish it.
Have the chief take the pearl from the lab and they will take it over to the giant clam that is out on the ocean.
The clam will take the blue pearl and the chief will then take the key and take it to the door. The key looks like a big black pearl.