Giant Crystal of Naica

A selenite beam longer than a school bus/Geology & Minerals

The Cave of the Crystals in Naica, Mexico, contains the largest natural crystals ever found. The biggest selenite (gypsum) crystal measures about 12 meters long and 4 meters in diameter, weighing an estimated 55 tonnes. The crystals grew over roughly 500,000 years in water saturated with calcium sulfate at a constant temperature of about 331 K. The cave is so hot and humid that humans can only survive inside for about 10 minutes without cooling suits.