Quartz is one of the most common minerals on Earth. It is composed of silicon and oxygen, the two most abundant elements in the crust of the Earth. Quartz comes in many colors including purple/violet (Amethyst); yellow and purple (Ametrine); yellow/orange (Citrine); pink (Rose Quartz); brown (Smoky Quartz); green (Prasiolite) and colorless (Rock Crystal). The various colors are due to trace elements added to the basic Silicon Dioxide formula. Quartz also has many attractive and collectable inclusions (see below) created by the addition of other minerals such as Actinolite, Gilalite, Lepidocrocite, Pyrite, Rutile, Tourmaline and many others. Quartz catseyes and stars are also available and are created by the presence of fine asbestos or rutile fibers. Quartz gems have been faceted in enormous sizes. The Smithsonian Institute (SI) has a perfect sphere of flawless Burmese Rock Crystal that is 12.75 inch in diameter and weighs 107 pounds. SI also has a 7000 carat faceted Quartz, a 2258 carat Brazilian Citrine, a 4500 carat Smoky Quartz and a 1362 carat Brazilian Amethyst!