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Turquoise
The name of the gem is apparently related to
the fact that r was brought to Europe from the Eastern Mediterranean
b> Levantine traders, generally known as Turks. It has
servec as an ornament for a very long time, having been used
b> the Egyptians some thousands of years ec. Nowadays,
it is one of the most controversial gems, because much of
the material sold has undergone so many different treatments
that its original appearance has been completely transformed.
Appearance On the rare occasions when it
has not beer interfered with in any way, it has a uniform
surface appearance almost like that of unglazed china or very
finegrained, homogeneous rock. It may be a strong blue color
but is more often pale sky blue, greenish blue or pale green.
It can contain narrow veins of other material, either isolated
or as a network; these are usually black or brown, though
sometimes yellowish brown.
It may also contain patches of whitish foreign
minerals, with occasional, minute crystals of pyrite. It is
used almost rough, in lightly polished nodules or, more often,
in the form of spherical or summarily rounded, polished pierced
stones (for necklaces and other items of jewelry). It is also
made into cabochons, carved gems, or figurines. When, as very
often happens, it has been impregnated with paraffin, the
surface appearance under a lens is distinctive, with small
whitish, opaque patches juxtaposed with and interpertrated
by bluer, translucent areas, sometimes set agains faint pattern
of larger, indented patches. Like all gi~which are basically
pastel in color, the richer-colored tyr are the most appreciated.
The preferred color is strong c blue, the pale greenish-blue
being less highly prized, a the pale green even less so. Given
the wide range in ha, ness for this gem, the hardest types
with values at leas* excess of 4-4.5 are obviously worth the
most.
Distinctive features Because the most striking
exterfeature of turquoise is its color, it is readily imitated
by types of similarly colored surrogates. Ceramic mater marble,
and nodules of other minerals (howlite, magnesw that have
been externally stained, artificially colored c< pressed
powders, and plastic are merely a few of the merous substitutes
currently encountered. As a rule, a ' negative criteria make
a rough, preliminary distinction p sible:
• It is not turquoise if it appears under a lens to
consis* numerous, minute grains of polygonal shape, juxtapo,
in an artificial manner, with a homogeneous blue or i erogeneous
light and dark blue or light blue and whi, color;
• It is not turquoise if it reacts in a matter of seconds
at the most, to a drop of hydrochloric acid, showing t~ strong
effervescence, a change in color, or obvious = face damage
(all this must be verified under a lens)
• It is not turquoise if it is warm to the touch, light
plastic, and burns with the characteristic odor of plawhen
touched by a thin piece of red-hot iron wire. Apart from these
distinctions, not even establishment of basic physical properties
(the hardness is extremely s - able, thus not characteristic)
is sufficient to identify quoise with any certainty and this
must, therefore, be le` experts.
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