The gem mine is run by the Building Company, and is located next to it, near the elevator in the Island of the Wannies. In there, lots of wannies work mining the gems that are later used in the GazoGem Refinery to make the GazoGem.
The mine has a great part of the surface covered with lava, from where the miners get the gems, with the aid of their gloves. Then they shovel them to a little train that leaves them in a place where they put in big boxes in a storage of the Building Company. There is also a little chapel where the Fragment of the Wannies is kept.
Besides being a source of gems for Twinsen to pay the Ferryman, the mine is where Twinsen needs to go to retrieve the fragment of the wannies. After finding the little chapel of Dark Monk in the mine, Twinsen enters and grabs the fragment, but just as he is doing it, a big light appears, and he hears a voice, which colud be of Dark Monk. Once he has the fragment, three wannies enter the chapel to fight him, and when he gets out, every miner turns hostile against him.
There is a crane which Twinsen can use to grab an otherwise unreachable clover box and leave it in the floor to pick it up.