Turquoise.

      Turquoise is one of the oldest gems to be set in jewellery, a famous early example being the four bracelets found on the mummified arm of Zer, Queen of Egypt 7,500 years ago. It was held sacred to Hathor, who was sometimes called Goddess of Turquoise. She was the cow from which creation sprang, and under whose protection all joy, love and merriment flourished.
             It was used by the Toltecs and Aztecs and, latterly, the Apache, Navajo and Pueblo Indians. Attaching Turquoise to an Apache bow protected the arrow from missing its target. The Navajo ground it for use in magical sand paintings, and held it emblematic of Mother Earth. Pueblos laid it as an offering where a dwelling was erected; it was also buried with the dead - one man was interred with nearly 9,000 Turquoise beads and pendants. The value of this jewel is clearly evinced by the fancy that anyone travelling to the end of a rainbow will find a Turquoise in the earth there. Zuni legend tells of a holy mountain of Turquoise from which the sky gains its colour.
             An early Hindu belief, echoed in Persia, held that great good fortune is attracted by looking at a piece of Turquoise immediately after seeing the New Moon, or by seeing the crescent reflected in it. Ancient Arabs claimed to foretell the weather by careful observation of the mineral's hue. Perspiration can be absorbed, making the stone an indicator of health in certain instances, and Turquoise gained a reputation for absorbing illness itself, leaving the invalid purified and free from it.
              Its supposed willingness to take on the suffering from another developed into superstitions such as belief in its ability of improving eyesight simply by gazing upon the stone. Claims were bold enough to include the cure of the blind. Carrying the jewel is still said to prevent migraine, a reputation surviving from the Middle Ages, and headaches due to eye-strain are held to respond well also.
              The evil eye is averted by Turquoise, and many animals, especially in and around Iran, still wear it to ward off demonic attack. Ancient Persian belief held it to protect a rider from falling from his mount. This has been extended to include protection from dizziness and vertigo. In the 14th Century it was reputed to protect thirsty, overheated horses from the agonies of drinking cold water. Tradition also regards it as particularly potent against the stings of scorpions, when powdered and drunk as a potion.
              In The Merchant of Venice, Shakespeare did credit the avaricious Shylock with some tenderness (albeit in bathos). When Tubal informs him of the theft of a particular gem by his daughter, and its subsequent bartering for a monkey, Shylock cries: "Thou torturest me, Tubal: it was my turquoise; I had it off Leah when I was a bachelor: I would not have given it for a wilderness of monkeys." The value of Turquoise as a lover's token was current since the Middle Ages: its power to change colour was used as an indicator of any alteration in the beloved's fidelity.

Turquoise usually occurs as nodules composed of myriads of minute crystals packed so closely as to be invisible to the naked eye - a cryptocrystaline structure. It is opaque, with a waxy lustre, and varies in colour, shading from green to blue. The blue hue derives from traces of copper, the green from ferric iron. The sky blue colour of the most valuable specimens is held to be powerfully representative of heaven and spiritual love.
             Many natural and tumbled specimens are nodular and somewhat lumpy in appearance, with dark, even black grooves concentrated around the hollows. An analogy with hills and streams would not be misleading. Turquoise comes mainly from arid regions, and is found in many parts of the world including Africa, the South West States of America, and the Near and Far East where it has been extensively used in China, India and Tibet. The name derives from the merchants who supplied Europe with it - the Turks. A very poor quality Turquoise has been found associated with China Clay in Cornwall, UK.
              Turquoise has been simulated by a wide variety of methods since the days of ancient Egypt. It is sometimes even ground to a powder and reconstituted - it pays to be discriminating in order to ensure purchase of a natural specimen.
              It is also somewhat porous and its colour can easily be artificially enhanced. If you prefer your jewels unadulterated, special care needs to be taken here because the practice is both very widespread and often notoriously temporary. Many inexpensive, poor quality stones quickly revert to their natural, unappealing state: some even fracture and fragment without apparent cause.
              Other specimens are processed specifically to clog all the pores so as to block the mineral's natural ability to change colour - an ability which has given rise to many of the ancient traditions regarding the stone's 'magical' colour changes.
             Turquoise is usually just too hard to carve with a pocket-knife. It is a phosphate of Aluminium, produced as rocks rich in the necessary elements decompose.