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Topaz
In ancient times, just about any yellow gem was likely
to be called topaz. The name itself may have been derived
from a Sanskrit word meaning "fire." The association
of topaz and the color yellow is Unfortunate, since
fine topaz occurs in colorless crystals, as well as
pink, blue, green, and a pleasing "sherry"
color.
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The
jewelry trade has created a host of terms for the sale
of yellow ¬gems. For example, we find "smoky
topaz," which is actually smoky quartz; "citrine
topaz," "Bohemian topaz," and "occidental
topaz which are all citrine; "Oriental topaz,"
which is yellow corundum Most of the stones sold as
"topaz" today are actually citrine. True top¬az
is labeled properly with only two modifying terms: "precious"
and" Imperial," the latter referring to a
Brazilian occurrence. |
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The
most important color variety of topaz is the range of yellow
and brown gems, mined chiefly at Ouro Preto, Brazil. Some
of this material ¬actually attains a bright-red hue. Golden-brown
topaz is the mw-¬expensive color variety, with large faceted
gems commanding prices several hundred dollars per carat.
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Topaz |
| Topaz
Related
to the brownish stones is pink topaz, because
it has been found that some sherry-colored and
yellow material will turn pink on heating. True
pink topaz does occur in nature, but is extremely
rare. A rare light-violet topaz color has also
been observed..
Colorless topaz is both attractive and inexpensive.
Proper cutting Can yield bright and sparkling
gems, but the lack of color reduces its ,rid and
keeps its price low. Blue topaz, on the other
hand, has become increasingly popular. This is
partly due to the surge in popular aquamarine.
Fine aquamarine has become so expensive and e
that blue topaz has begun to find wide use as
a substitute. Most topaz is fairly pale, but some
material can apparently be turned a deep color
by irradiation with gamma rays. Green and greenish-yellow
gems are occasionally seen in the gem trade, but
these are rare and not generally known to the
buying public. There is currently no effective
'1yuishing test for irradiated blue topaz or heat-treated
pink topaz. Purchase of such stones should always
be accompanied by some statement Indicating natural
origin or prior treatment.
Topaz
usually forms late in the crystallization of rocks.
It is typically rd in pegmatite dikes, and crystals
can reach enormous size. den-brown crystals up
to a foot in length are known, but even these
dwarfed by the 100-pound behemoths found in Brazilian
deposits. of these crystals are perfectly formed
and nearly completely transparent.
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Topaz
is very hard, 8 on the Mohs scale, so it wears well in jewelry.
- only drawback is a well-developed cleavage, making the
cutting of topaz gems a tricky business. A casual blow to
a cut topaz could cause it to split so rings should be treated
with some care
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