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Postage stamps dedicated to Topaz!
image location - stampmin.home.att.net |
Topaz under a microscope!
image location - microscopy.fsu.edu |
Topaz is currently the best selling colored gemstone in the U.S. Its
popularity is based not only on its beauty, but also on its low cost
when compared to other blue stones like aquamarine, sapphire, tanzanite
or iolite. The lower cost is a direct result of the overabundance of
this beautiful blue stone. Interestingly, though, this stone is rarely
found in nature in a blue color, except in the lightest shades. Topaz
normally occurs in a wide variety of colors, including varying shades of
red and pink, orange to gold, as well as colorless to light blue.
Virtually all colors are represented except for purple. Green topaz,
another color induced by man, has recently entered the market. Topaz
prices will range widely from blue topaz, which is easily found for
under $30 per carat, to its more expensive pink or red topaz cousins
which will sell for over $1,500 per carat. Most other shades will range
in between, except for clear or 'white' which is less expensive than
blue and is sometimes used as a diamond substitute.
Brazil is the world's leading producer of topaz, occasionally
providing huge transparent crystals sometimes weighing several
hundred pounds. The largest cut topaz is over 20,000 carats. Although
they don't produce crystals of the immense size as are sometimes found
in Brazil, large deposits are also mined in Mexico with sizable
deposits in Sri Lanka as well. In the United States, topaz is found
in Texas, Colorado and Utah in moderate quantities with lesser amounts
found in New Hampshire, Maine, South Carolina, and California. Limited
deposits of this precious stone are found in various countries
throughout the world, including Pakistan, Nigeria, USSR, Zimbabwe,
Germany, Australia, and Burma, but not many locations provide the
quantity or quality necessary for the gemstone industry.
| Composition | Al2SiO4(F, OH)3 | Class | silicate |
| Specific gravity | 3.4 to 3.5 | Refractive Index | 1.61 to 1.64 |
| Birefringence | weak | Pleochroism | weak to moderate |
| Cleavage | perfect | Fracture | conchoidal, brittle |
| Luster | vitreous | Transparency | transparent to translucent |
| Streak | white | Fluorescence | ocasional / mild |
| Crystal system | orthorhombic | Twinning | very rare |
| Hardness | 8 | Dispersion | .014 |
Color
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Virtually all blue topaz is irradiated and
heat-treated in order to produce the color we are accustomed to
seeing. The blue colors we are familiar with were not created
until the coming of the nuclear age, and they are generally created
through various methods using different types of radiation. The
three more popular processes include exposure to low level gamma
radiation, followed by heating; bombardment by high powered
electron beams in linear accelerators; and exposure to high levels
of radiation inside nuclear reactors. The last two methods leave
the stones radioactive for a short period of time (a few weeks for
the former treatment to a few months for the latter). After the
gems have 'cooled off' to safe levels, they are put on the market.
Low level gamma radiation is not often used any longer, as it will
not produce the deeper colors of the other two methods.
Images © theimage.com |
| Crystal habit | Topaz can be granular and massive. It is most commonly found as euhedral prismatic crystals terminated by dipyramids, first and second order prisms, and basal pinacoids. It often shows vertical striations on the prismatic faces. |
Other
| The natural coloration of the gem is dependent
on the ratio of the compounds and impurities. Low concentrations
of fluorine tend to make the stone yellow or pink, rather than
clear or light blue. Traces of chromium will turn the stone pink
or red. The creation or destruction of a 'color center' through
radiation or heat, will produce the darker blues.
Images © theimage.com |
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In ancient times, the name 'topaz' was used to refer to any
yellow stone. In 1747 'topaz' was first used to describe the mineral
that we know today. Even today one often encounters the terms 'smoky
topaz' and 'madeira topaz' being used for smoky quartz and citrine
quartz. Until the 18th century, the name 'topaz' was often used in
referring to our present day mineral peridot. The name 'topaz' is
thought by many to be derived from the ancient Sanskrit word 'tapas'
meaning fire. Another theory, which was first put forth by Pliny in
the first century AD, is that the name 'topaz' was derived from the
Greek word 'topazos' or 'topazion' meaning to seek. Topazos was also
the name of an island in the Red Sea, now known as 'Zeberget', or the
'Island of St. John', which is thought to have been an ancient source
for the gem peridot, but not true topaz. The term 'imperial topaz'
originated in Russia in the 19th century, when topazes with pink
tones were discovered there and proclaimed by the Czar to belong only
to himself and the royal family, and others to whom he had given it as
a gift.
Topaz was one of the stones in the 'Breastplate of Judgement' of
Aaron, described in the bible. Historically, topaz has been
thought to give long life, good looks and inteligence. It is
also thought to given protection from poison by changing colors
in its presence, It gives protection from disease and sorcery.
The ancient Greeks believed that it had the power to increase
strength and make its wearer invisible in times of emergency.
Its mystical curative powers waxed and waned with the phases of
the moon. It was said to cure insomnia, asthma, and hemorrhages.
