In the thirteenth century turquoise was named after the French words 'pierre turquoise' meaning Turkish stone.  This is thought to have arisen from a misconception that turquoise originated in Turkey when in fact it originated in Persia and only entered Europe through Turkey.

Turquoise is one of the oldest known gemstones and was being mined by the Egyptians in the Sinai as early as 5,500 BC.

The blue colour of turquoise was believed to have powerful metaphysical properties by many ancient cultures.  In ancient Mexico it was reserved for the Gods and could not be worn by mere mortals.  In Asia, turquoise was considered to be an effective protection against the evil eye and in Tibet today, it is by far the most popular of all gemstones used for personal adornment and still plays an important part in religious ceremonies.  In the South West of the United States the Apache Indians believed turquoise would help warriors and hunters hit their targets more accurately if their spears or arrows were tipped with a piece of this gemstone.  The Zuni tribe believed it protected them from demons and it was also believed by some that it had the power to protect the wearer from injury should they fall, especially from a horse and furthermore, turquoise also made the horse more secure on its feet.  

Turquoise was worn around the necks of Egyptian Pharaohs and adorned the ceremonial dress of early Native American Indians.  It has been attributed with unlimited healing powers as well as promoting the wearer's status and wealth.  Turquoise remains a sacred stone to many of the American Indian tribes.  They consider it to be both a protective stone and a bestower of goodness.

Turquoise was so highly valued that all seventy nine emeralds in the crown that Napoleon I gave to his consort Empress Marie Louise were replaced with Persian turquoise cabochons.

Turquoise is one of the crystal healing master gemstones.  It is said its powers can benefit the entire body, with special strengths in healing ailments of the immune, respiratory, waste and skeletal systems.  Healers recommend it for detoxification of alcohol, poison, pollution or radiation, for treatment of high blood pressure, asthma, infections and dental problems.  In relation to the mind, turquoise is said to be a stone of communication and is used for those who have a fear of public speaking.  It is also believed to improve the mental state overall by increasing serenity, creativity, empathy, positive thinking, sensitivity, intuition, happiness and wisdom.  Turquouise emanates a purifying energy which tends to dissipate negativity.  It acts to induce wisdom and understanding and to enhance trust, kindness and the recognition of beauty.  It is said to promote spontaneity in issues of romance and to stiumulate the initiation of romantic love.

Turquoise was used in ancient times to insure property and to protect against accidents.  It has been esteemed by the Tibetan shamen as holding both a spiritual and protective property.  It has been used in shamanic ceremonies and in the sacred valley of Shambhala.   

Turquoise is one of the birthstones for December and the anniversary gemstone for the 11th year of marriage.

The most important producers of turquoise are Iran, South West United States, Tibet, China, Afghanistan and Australia.

Turquoise is graded 5 to 6 on Mohs scale of mineral hardness.

The following links offer further reading on turquoise

http://en.wikipedia.org/wiki/Turquoise
http://www.gemologyonline.com/turquoise.html
http://www.gemstone.org/gem-by-gem/english/turquoise.html
http://www.gemstoneeducation.com/Turquoise.htm