Topaz is a fluorosilicate. Fluorosilicates include aluminum, fluoride, silicon and oxygen. They also have other trace elements such as chromium that can cause different colors within the Topaz. Topaz are known to have color centers and while color centers are not fully understood, the color of Topaz can change, usually with the help of intense heat or radiation.
Topaz comes in a wealth of beautiful colors including blue, pink, red, lavender, yellow, brown, orange, colorless and green. It should be noted that both red and lavender are usually extremely rare colors. Colorless topaz and yellow are fairly common.
It should be noted that Blue Topaz is one of the most popular gemstones sold commercially, usually due to its affordability and beautiful rich hues. The vast majority of Blue Topaz is treated, usually with heat or radiation to enhance the color of the Topaz. Usually Blue Topaz is formed from colorless Topaz, but it can be created from Blue or even yellow Topaz.