Amethyst Mine

This is the fourth mine and is the rarest: The Amethyst Mine! A lot valuable, but was released on the six updates before the new mines was released. This mine can equipped with a recruit or guardian manager, but also the prisoners clothes was changed on the special update to improve their equipment. And the mine can get even more coins, but gets more money and prisoners mine for amethyst gems and or shards in this mine. Upgrades the Emerald Mine, and makes more moneys per second fast. This mine can equip a guardian to help get more power in the cells.

Mine
It is the richest like the crystal mine and it's still valuable.