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Jamming Gems Topaz Information
Topaz
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General Information:
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. |
Common Treatments and Lab Created
Forms:
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.
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Physical Properties:
Moh's Scale Hardness: 8
Specific Gravity: 3.4-3.6
Refractive Index: 1.606 - 1.638
Fracture: conchoidal
Crystal Habit: commonly as euhedral prismatic crystals terminated by
dipyramids, first and second order prisms, and basal pinacoids. Frequently with
vertical striations on the prismatic faces. Also appears in crystalline masses.
Colors: commonly colorless, but can be found in light to medium blue,
yellow/orange/pink/red/violet with or without brown tone, brownish green,
brown.
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