Name your Palette: Description: Natural Zircon is known for its distinctive beauty and occurrence in a broad range of colors and has sustained the interest of gemologists for years owing to its variation of specific gravity and refractive indices. But most curious and less known are the tenebrescent properties of some zircons. Also known as reversible photochromism, tenebrescence refers to the ability of minerals to change color when exposed to the natural radiation in sunlight. http://www.multicolour.com/gemstones/zircon.html