Topaz

Topaz is the birthstone of the month of November. The stone has a long history, noted as a gem used in the ‘Breastplate of Judgement’ of Aaron, described in the bible (Exodus: xxviii, 15-30). The majority of topaz is colorless, then treated to be blue in color. Natural untreated topaz can be found in champagne, blue, pink, and imperial. It is rare to find a natural blue topaz that has no treatment, as with pink, while it is found, it is very rare and expensive. Imperial topaz is the most sought after color of topaz, it is a rich golden color that generally has no treatment.

Topaz (Al2SiO4(F,OH)2) is an aluminum fluorosilicate. The different color of topaz are caused by variations in the amounts of F,OH. Topaz has “color centers” which when naturally radiated give it its variety of colors. Often times this “color center” is not stable and the color can fade quickly just when exposed to sunlight.

Origin

Brazil is the largest supplier for topaz. Other deposits are in Afghanistan, Australia, China, Japan, Madagascar, Mexico, Myanmar, Namibia, Nigeria, Pakistan, Russia, Sri Lanka, Ukraine, United States and Zimbabwe. Natural light blue topaz can be found in England (Cornwall), Northern Ireland and Scotland.

Properties, Treatments & Lab Created

Topaz is rated an 8 on the Mohs scale.

Colorless or lightly tinted natural topaz is irradiated to change the color to blue then heated to stabilize the change. London Blue topaz’s color is created by neutron bombardment in a nuclear reactor, while Sky Blue topaz gets its aqua-like color from electron bombardment in a linear accelerator. Mixing different combinations of those two treatments creates the swiss or electric blue color found in topaz. Residual radioactivity is left on the gem after neutron bombardment, therefore the gems must be held up to a year before they can be worn. Most pink topaz is heat treated from yellow stones that turn pink when heated. Topaz can also be treated to give it a “mystic” or rainbow appearance. This is done by coating, either by a PVD (Physical Vapor Deposition) which is a thin optical layer placed on the stone, or through a process called diffusion. In diffusion, chemical agents in powder form are wrapped around each stone or group of stones forming a “cake” and heated at very a high temperature in a furnace. The topaz and the chemical agents bond together forming a permanent coloration of the surface.

At this time there is no lab form of topaz on the market.