The Amethyst mines in Brazil are considered the best in the world. To get there you must get to Rio De Janeiro, fly south to Port Alegre, drive 3 hours to Solidad (near Uruguay), and then it’s a 1 hour drive to Amethyst del Sul .
There are hundreds of working mines in the area. All are mined by hand, though small motorized carts may be used to remove excess rock. The cavities are large gas bubbles formed in the cooling larva a millennia ago, the cavities were filled with water and dissolved minerals permeated through the rock. In time these minerals crystallized in these cavities, lining them with a silica layer (in this case Amethyst). These geodes are in a continual state of development as long as the there is moisture present in the basalt.
After blasting the rock, the miners locate the undamaged geodes, they then drill a small hole to determine the quality and shape of the amethyst cavity. It can take many hours just to remove a geode. It must be very carefully chipped out of the host rock with minimal damage as this could severely effect the final price. They are then taken to workshop in town where they are cut and polished.