Precious Topaz refers to yellow to red colors of this gemstone. Any topaz containing a hint of red is referred to as 'imperial' topaz, most of which comes from the historic gold mining town of Ouro Preto in Minas Gerais, Brazil. Some topaz is heated to remove the yellow component of the color, leaving only the pink tone. Larger stones tend to be long and narrow because fractures in the rough commonly run lengthwise down the crystal.
Blue Topaz has become a standard of the jewelry industry along with garnet, citrine and amethyst. Since scientists discovered that irradiation would turn clear topaz into vibrant shades of blue, the supply has been able to keep up with demand and prices have been very affordable. There is a natural counterpart to blue topaz, but it is rarely seen anymore, since the colors pale when displayed next to their irradiated cousins. Recently, new processes have been used to coat clear topaz with other colors creating a whole new set of affordable gems. These newer processes are merely a surface coating, whereas the blue color is throughout the stone.
Topaz has a hardness of 8 making it superb for all types of jewelry.
Treatments: Irradiation to create blue color. Diffusion and coating to create assorted colors. Heating to remove yellow.