This stone is becoming increasingly rare and costly because the finest material comes from Iran. Despite its fragility it is much prized and never seems to go out of fashion.

It is an opaque mineral consisting essentially of phosphates and is of a colour ranging from sky-blue to apple-green. The best turquoise is, however, dark and should be totally free of any black veins or white specks. It must be cut en cabochon. It is sold by the carat, a very rare procedure for an opaque stone.

Turquoise is an excellent investment, but if it is to retain its value it should be cleaned at least once a year with diluted ammonia liquor. This restores its original colour which otherwise tends to become greener with age. It should never be stored with other jewelry or cosmetics.

As I mentioned earlier, the finest turquoise comes from Iran, b specimens from Sinai and China are almost as beautiful. Russian and American turquoise is of a decidedly poorer quality.