Imagine crystals that weigh over 55 tons, make humans look like dwarfs, and dwarfs look like ants. The Giant Crystal Project has a collection of information on abnormally large crystal growths. It’s definitely worth a look.
In 2000, geologists at the Naica zinc mine in Mexico discovered the largest crystals ever found in a cave 300 meters beneath the Chihuahuan Desert.
When magma underneath the mountain cooled and the temperature dropped below 58 degrees Celsius, the anhydrite began to dissolve. The anhydrite slowly enriched the waters with sulfate and calcium molecules, which for millions of years have been deposited in the caves in the form of huge selenite gypsum crystals.