Turquoise is a particularly problematic stone when it comes to verifying its authenticity. It consists of a phosphate of aluminium, colored by copper and traces of iron. Some gemologists believe that the beautiful blue color is produced by a complex ion formed from copper and ammonium. The finest colored material is mined and worked in Iran; its colors range from the highly desirable sky blue to a bluish green.
The color of turquoise is sometimes affected by the acid perspiration of certain wearers. When this happens, the stone will become green or greenish, as it also does if it becomes too warm. The color is also affected by the alcohol content in perfume, hair sprays and cosmetics. Turquoise got its name from the Turkish merchants who first carried this beautiful and very desirable blue stone to Europe for trade. Trudging the commercial trade routes from the East, they drove great camel caravans burdened with sacks of exotic, aromatic spices, bolts of cloth encrusted with gemstones and interwoven with gold and silver threads, and all kinds of jewels and other treasures. The stones were first exported to Germany, where they became known as Turkisher Steins, which translates as "Turkish stones". When the stones reached France, the German name became translated into Pierre turquoise - stone of Turkey.
Turquoise was once credited with the ability to overcome malevolent glances from the Evil Eye. Even today, the citizens of many Middle Eastern countries weave turquoise beads into the manes and tails of beasts of burden such as camels, mules and oxen to bring good luck and assurance that the animals will surefooted. Turquoise beads are also believed to protect a horse if it becomes overhead by too much exertion - and to shield the rider from harm. From the thirteenth century, this stone became the horse man's talisman and it was at this time that a certain man called Volmar wrote: "whomsoever owns a true turquoise set in gold will not injure any of his limbs when he falls, whether he be riding or walking, so long as he has the stone with him."
To the Persians, the intensity of the sky-blue stone foretold the kind of weather to be expected that day. A dazzling blue color seen during the morning foretold a fine day, and a happy one. The Persians also say that to have good fortune and repel evil, a man must see the reflection of the new moon on either a copy of the Koran, the face of a friend, or on a turquoise stone.