Wednesday, 27 February 2013

The Attractive Collection of Crystal And Gems

TANZANITE The purplish-blue gem variety of the mineral zoisite is tanzanite. It was found in northern Tanzania in 1967 and is remarkable for its displays of rich blue, magenta, and yellowish grey. Many crystals are greenish grey and are heat treated to the more attractive blue.

WITH OVER 3,000 SPECIES of minerals to choose from, the potential number of gems would appear at first to be very large. But crucial factors such as hardness, durability, and rarity reduce the number of commercial gems to a few tens. Many people collect rarities that are not in general circulation. They may seek the rare colours or exceptional sizes of common gems, or cut examples of minerals too soft or fragile to wear in jewellery. 

Synthetic ruby Crystal

For example, blende and sphene are available in reasonable quantities but are too soft for constant wear. Benitoite is durable enough to be worn but is too rare to be generally available.

What is it worth?

THE MARKET VALUE OF GEMS plays a large part in persuading people to buy them. Fashions change, so that gems that were priceless in the 19th century may no longer be so and vice-versa. 

WEIGHT IN BEANS The seeds of the carob tree are of remarkably constant weight, and they were used for many centuries as a standard for comparing the weights of precious stones. Later, a standard weight similar to that of the carob seed was used, and it was called the carat. For some time it was slightly different in different trading centres, but early this century a metric standard of 0.2 g (0.006 oz) was agreed internationally.
Further back in time, lapis lazuli, turquoise, agates, and emerald were prized. From the fifth to the 14th century A.D. stones were not often cut because this was thought to destroy their magic. Since then however, more and more stones have been cut to enhance their beauty, and they are traded to satisfy people's desire to display their style or wealth. 

Since medieval times diamond, ruby, pearl, emerald, and sapphire have been popular, while the popularity of species such as topaz, garnet, and aquamarine has been erratic.

Writer –Dr.R.F. SYMES and Dr.R.R. HARDING

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