Re: Irradiated Gemstones

[Susan Gawarecki <loc@icx.net>]

>From http://www.tradeshop.com/gems/enhance.html:

Irradiation - Colorless topaz is irradiated in large quantities and then
heat treated to produce various shades of blue. Yellowish diamonds are
often irradiated to produce a wide variety of colors. Other stones, such
as tourmaline, are sometimes irradiated to enhance or produce new
colors. In many cases, the effects of irradiation are somewhat unstable
and can be reversed by heating.  

Heat treatment - Many gems are routinely heated under controlled
conditions to improve color (aquamarine, sapphire, ruby, tourmaline),
alter color (sapphire, amethyst to citrine, topaz, zircon), or improve
clarity (sapphire, ruby). Since natural heating also occurs (e.g., in
volcanic areas), the artificial effects are sometimes indistinguishable
from natural effects. In most cases, the results of heat treatment are
permanent. 

And from http://www.inetworld.net/rbusch/fgms/impgems.htm:

Gamma Radiation - The most common means of altering gemstone color by
radiation is with gamma rays (cobalt 60 radiation). Gamma rays release
electrons from their normal location in the gem. The color change
depends on where the electrons relocate and on the charge of the atoms
near them. These factors control the way the stone absorbs light, and
thus they dictate its color. 

There are no guarantees of success for gemstone enhancers because it is
impossible to predict how irradiation will affect a stone. Certain
mineral impurities must be present and the radiation must shift
electrons to desirable color-producing
locations. Normally, many gemstones must be irradiated in order to
obtain a few stones that are altered to the desired color. 

Topaz, Al2[SiO4](OH,F)2, which is colorless in its pure mineral form, is
one gemstone suitable for irradiation. When exposed to cobalt 60
radiation, the stone may change to a cinnamon brown color, but this tone
normally fades over
several months when exposed to light. Recently, however, gem dealers
have developed the technology to produce a brilliant and permanently
blue topaz through irradiation, equal in its attractiveness to rare
natural blue topazes. An
irradiated blue topaz exhibits all the chemical and optical properties
of the natural stone, and can be distinguished only through an
analytical process of measuring the light emitted by a gemstone when it
is heated. 

Irradiation is also used to change quartz (clear and colorless in its
pure mineral form, SiO2) to the more attractive and valuable smokey
quartz. But this transformation only occurs when the colorless quartz
contains traces of aluminum, and ultimate success depends on where the
electrons settle after irradiation. Amethysts can be produced by
irradiating quartz that contains iron impurities, but attractive
amethysts occur so abundantly in nature that it is not commercially
economic to create them synthetically. 

Diamonds, C, which occur naturally in many colors, can be irradiated to
produce different hues. Irradiation can change lightly tinted diamonds
to brilliant yellows or greens. However, the dealer irradiating such
expensive stones as diamonds is
taking a heavy risk, since a valuable, lightly tinted diamond may turn
out a muddy brown. 

Not all artificially induced color changes are permanent. Kunzite, a
lavender variety of spodumene, LiAl[Si2O6], emerges a brilliant green if
bathed for 15 minutes in cobalt 60 radiation. The radiation changes the
electrical charge of manganese ions responsible for the gem's color from
+3 to +4. But when exposed to light, the +4 ions begin to add more
electrons to their structure and the stone reverts to spodumene, drab
and colorless in appearance. 

Heat Treatment - Irradiating gemstones to change their color is a
relatively new process, but altering their internal structure by heat
has been practiced for many years. Stones are often heat-treated at the
mines by persons who developed simple procedures through
experimentation. 

Among the stones that benefit from heat treatment is aquamarine, which
occurs naturally in many colors -- yellow, yellow green, blue green, and
blue -- depending on the atomic charge and location of the iron atoms in
the mineral. Heat that
changes the atomic charge of iron atoms from +3 to +2 transforms a
yellow aquamarine into a more valuable blue aquamarine. 

Comment: As I recall, cubic zirconium turns pink when irradiated (there
was a big "pink ice" jewelery craze a few years back).  


-- 
==================================================
Susan L. Gawarecki, Ph.D., Executive Director
Oak Ridge Reservation Local Oversight Committee, Inc.
136 S Illinois Ave, Ste 208, Oak Ridge, TN 37830
Phone (865) 483-1333; Fax (865) 482-6572; E-mail loc@icx.net 
==================================================

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