Citrine is any quartz crystal or cluster that is yellow or orange in color. Although often cut as a gemstone, natural citrine is actually somewhat rare. Most citrines on the market have been heat treated. Specimens of low grade, inexpensive amethyst or smoky quartz are often cooked at high temperatures to produce the more profitable orange yellow citrine. Citrines whose colors have been produced by artificial means tend to have much more of an orange or reddish caste than those found in nature, which are usually a pale yellow. Much of the natural citrines may have started out as amethyst but heat from nearby magmatic bodies may have caused the change to citrine. Interestingly, a popular gemstone on the market is a mixture of half amethyst and half citrine and is given the name ametrine.