The name of the gem is apparently related to the fact that it was brought to Europe from the Eastern Mediterranean by Levantine traders, generally known as Turks. It has served as ornaments for a very long time, having been used by the Egyptians some thousand of years BC. 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:
It occurs as microcrystalline aggregates in the form of irregular, lobed or indented nodules or in thin strips (usually of no more than a few centimeters), which are more compact and strongly colored at the center, lighter and porous on the outside. It is blue-white to sky blue, light greenish blue to light green. It is generally opaque, only thin pieces being translucent.



Appearance:
On the rare occasions when it has not been interfered with in any way, it has a uniform surface appearance almost like that of unglazed china or very fine grind, 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 mineral; with occasional minute crystals of pyrite. It is used almost rough in lightly polish nodules or, more often, in the form of spherical or summarily rounded, polished pierced stones. 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 juxtexposed with and interpenetrated by bluer, translucent areas, sometimes set against a faint pattern of larger, indented patches. Like all gems which are basically pastel in color, the richer-color types are the most appreciated. The preferred color is strong sky blue, the pale greenish-blue being less highly priced, and the pale green even less so. Given the wide range in hardness for this gem, the hardest types with value in excess of 4-4.5 are obviously worth the most.



Distinctive features:
Because the most striking external feature of turquoise is its color, it is readily imitated by all types of similarly colored surrogates. As a rule, a few negative criteria make a rough, preliminary distinction possible:
1.it is not turquoise if it appears under a lens to consist of numerous minute grains of polygonal shape, juxtaposed in an artificial manner, with a homogeneous blue or heterogeneous light and dark blue or light blue and whitish color.
2.it is not turquoise if it reacts in a matter of seconds, ten at the most, to a rock of hydrochloric aced, showing fairly strong effervescence, a change in color or oblivious surface damage( all this must be verified under a lens).
3.it is not turquoise if it not warm to the touch, light like plastic, and burns with the characteristic odor of plastic when touched by a thin piece of red-hot iron wire.



Occurrence:
In ancient times, turquoise was mined in the Sinai Peninsula and Iran, while certain Central American peoples, the Aztecs in particular, extracted it in what is now known as New Mexico. The best quality turquoise still comes from Iran, but in relatively small quantities. Recently deposits in the United States (New Mexico, Arizona, California, and Nevada) have been increasingly exploited. Much of the material extracted from the sources is of low quality, but it is used, never the less, after being treated to improve its hardness, consistency, and color.



Value:
Because it has been fashionable for a number of years, turquoise is quite highly price in relation to comparable non transparent gems, although it is fairly plentiful on the market. Its value exceeded only by lapis lazuli and top quality jadeite jade.