Cave of the Crystals or Giant Crystal Cave (Spanish: Cueva de los cristales) is a cave connected to the Naica Mine at a depth of 300 metres (980 ft), in Naica, Chihuahua, Mexico. It takes the form of a chamber within the limestone host rock of the mine, and is about 109 metres (358 ft) long with a volume of 5,000 to 6,000 cubic metres (180,000 to 210,000 ft3). The chamber contains giant selenite crystals (gypsum, CaSO4 · 2 H2O), some of the largest natural crystals ever found.