Topaz is an extremely versatile gemstone and is found in large clean crystals. The most commonly Topaz found on the market is blue since almost all Topaz has undergone irradiation treatment to change the colour. Topaz of any type is an excellent jewelry stone due to its hardness (8 on the Mohs scale) and high refractive index. Topaz is also available in numerous cuts and sizes all at affordable prices. Topaz comes in many colors, including clear, brown, yellow, orange, red, pink and blue. The blue topaz, with a pale to a medium blue color created by irradiation, can be found in huge sizes at affordable prices. The excellent golden-yellow variety, known as imperial topaz, is relatively scarce and very collectible.