Two miners working for Industria Peñoles discovered Mexico’s Cueva de los Cristales (Cave of Crystals) by accident while excavating a new tunnel in 2000. They were amazed by the sight of massive crystal structures.
The crystals measured up to 12 meters long (over 36 feet) with a single crystal weighing approximately 55 tons. These were the largest crystals that anyone had ever seen in the cave.
Millions of years ago, volcanic activity filled the mountain with anhydrite, a water-less form of gypsum. As magma eventually cooled, the anhydrite began dissolving, enriching cave waters and allowing gigantic crystals to form. Amazingly enough, the size of the crystals has no limit and given enough time will grow to even larger proportions. There are very few other places in the world where such crystals have been so well preserved in their purest of forms.
Giant Crystal Cave was an inhospitable place. Not only did the air temperature climb as high as 113 degrees Fahrenheit (47.1 degrees Celsius), but the humidity levels also reaches close to 100%. Because of these harsh conditions, scientists and researchers need to wear special cooling suits, and can spend no longer than a 30-45 minutes within the cave. Peñoles carefully restricted access to the Cave of Crystals, to protect not only the crystals but also their visitors.