Tiger’s Eye is a form of Chalcedony quartz, but is what is a known in mineralogy as a pseudomorph. The term comes from the Greek for "false form." Pseudomorphs form when one mineral replaces another. It began as the fibrous blue mineral called Crocidolite, which is made up of iron and sodium. The Crocidolite was gradually transformed into when quartz becomes embedded between the fibers of Crocidolite. This process can result in two different gemstones: a blue stone called Hawk's Eye or the golden brown stone called Tiger's Eye. Gentle heating can turn Tiger’s Eye a rich red color. In the course of the process, the Crocidolite is completely dissolved. But the quartz takes on the fibrous formations and this creates the parallel lines within the gem which gives it that effect of shifting plays of light; it is one of the "chatoyant" gemstones. Chatoyancy exhibits a changeable silky luster as light is reflected within the thin parallel fibrous bands.