Topaz is a transparent gemstone that's durable, brilliant, and has a vitreous luster. Due to its remarkable hardness, it is able to withstand most scratching. To amplify its brilliance, it's best that the stone has a step cut or a scissor cut. Colorless versions of topaz with either of these cuts can serve as a cheaper alternative to corundum or diamond.
Topaz has either two phase inclusions or three phase inclusions. Two phase inclusions consist of tear-shaped cavities containing gas bubbles and liquid. Three phase inclusions consist of gases, liquid and small crystals. These stones also might have cracks, streaks and veils.
It comes in a wide assortment of natural colors such as yellow, yellow-brown, orange-brown, pinky brown, light to medium red, blue and colorless. The most expensive and desirable colors for topaz are sherry topaz, precious imperial topaz, and pink topaz. Sherry topaz is a reddish orange color which is normally confused with citrine. Precious imperial topaz is a fine apricot-orange color. Pink topaz comes in a variation of pale pink and violet-pink.
Topaz can also be treated to give it an intense color (or to change its color to be a more natural color) and eliminate any inclusions. When it's irradiated, topaz can become a light sky blue, a vibrant Swiss blue and a dark gray-blue called London Blue topaz. Diffusion-treated topaz is either deep green or blue-green.
Hardness: 8 Mohs
Specific Gravity: 3.49-3.57
Refractive Index: 1.609-1.643
Crystal Form: Most topaz crystals are prismatic and they have characteristic eight-sided cross sections with striations which are parallel to the length.