Topaz is an aluminum silicate that contains fluorine and hydroxyl. In its pure form it is colorless (white). Impurities are what cause variations in color.Topaz ranges from colorless (white) to yellow, orange, red-brown, light to dark-blue, pink to red, violet and light-green. This is the reason why it can be mistaken for many other gemstones. Naturally colored topaz gets its color from iron and chromium; the impurities cause color, whereas pure topaz is colorless. Most unadulterated topaz is colorless or pale blue. The most rare and valuable topaz is yellow, or pink to reddish-orange, and is known as "imperial topaz" or "precious topaz". Topaz is transparent to translucent. It exhibits high clarity with few inclusions, so topaz gemstones can be examined by the naked eye and found to be "eye clean", which means that no imperfections can be seen. Topaz is highly prized for its brilliance and vitreous (glassy) luster.