ABSTRACT
The cave contains some of the largest mineral crystals in the world—up to 12 meters long. These crystals are selenite, a transparent form of gypsum, which has the composition hydrated calcium sulfate. Large crystals had been found in other caves in the Naica Mine, but the discovery of Cueva de los Cristales was much more spectacular. The study of crystals and their formation is termed crystallography. Crystals may consist of a single element but, more commonly, they are compounds of two or more. Nucleation is a kinetic process. Small nuclei composed of just a few atoms form relatively quickly compared with larger crystals. Temperature is a key factor affecting crystal growth because at elevated temperatures atoms are very mobile, which allows crystals to grow efficiently and often leads to large and well-formed crystals. In 1929, Linus Pauling formalized some fundamental principles of ionic and covalent crystal structures, called Pauling’s Rules.
