The Naica Mine is located in Naica, Mexico, and is known for its giant crystals of selenite. The Mine is a lead, zinc and silver mine operated by Mexico’s largest lead producer.
Some caverns found during the operations have crystals of selenite (gypsum) up to 4 feet (1.2 m) in diameter and 50 feet (15 m) long. These crystals are some of the largest ever found.
They were formed by hydrothermal fluids emanating from the magma chambers below. Unfortunately, this isn’t a place you can visit unless you work there, as the caves are closed to the public.