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Long ago, the Persians regarded emeralds and rubies as being more precious than diamonds, and we have evidence from various writers of different ages that stones such as opal and amethyst were esteemed much more highly than they are today. Cellini recorded in the Sixteenth Century that rubies were worth eight times the price of diamonds, while today the Chinese have little use for diamond and regard fine jade as being of much more worth. The finest qualities of Chinese jade are seldom seen outside China, for the Western peoples have not been trained to recognize the different shades and qualities which make up the wide range of this stone.

Precious stones, however, always have a considerable value based on their actual rarity, and unless we all relapse into thinking only in terms of guns, airplanes, and bombs, there will always be some who both appreciate and can afford to buy these unique products of nature. As for jewel stones other than the so-called precious varieties, these fluctuate considerably in value since their supply is seldom limited. During the last few years, prices have risen appreciably. Certain varieties, such as good quality star stones, kunzites, alexandrites, and aquamarines always command good prices; others, such as garnets, amethysts, moonstones, and peridots are the victims of the whim of fashion and their values consequently vary over the years.

The only notable exception in which the unit weights mentioned are not employed is in the calculation of the weight and value of natural pearls. Here, the pearl grain is used since a smaller unit is more convenient. Pearls are generally small in size and their specific gravity is low; a ten grain pearl of fine quality is rare and obtains a high price. The unit used, the pearl grain, is exactly one quarter, or .250 of a carat. Thus four grains equal one carat.

Prices of gem stones, including the cheaper varieties, vary so much that it would be futile to try to give any guide which would be of any practical value. Fashion and demand are the chief factors which causes these fluctuations in normal times, but abnormal economic and financial conditions due to war and sudden depressions also have a considerable bearing on commercial values. In such times, when the value of paper currency and other normal forms of wealth become dubious, there is always a great demand for diamonds and other precious stones since their worth is recognized internationally and they are also easily portable.

In India, originally the source of most of the precious stones, a weight known as the rati was used. This corresponded to the weight of the black seed of the abrus precatorius, which was something between the present half a carat and seven-eighths of a carat. The weight varied very considerably in different districts and at different times; for example, in the year 1827, one rati was equivalent to 2.114 grains Troy, while in 1896 it equaled only 1.88 grains Troy. In the Golconda district, once a rich source of the finest and largest diamonds, the mangelin was used as the unit of weight. According to Tavernier, this was equal to 1.375 carats. Now, the metric carat is used throughout India, as it is in nearly all countries where important dealings in precious stones take place.

For many centuries, a carat of no very definite weight was in general use; it was not the metric carat, and it had no definite relation to any constant weight or measure. As the years passed, the number and value of stones which came on the market increased. Their use in jewelry became more general, and attempts were made to fix some recognized universal standard of weight by which values could be determined. In the year 1871, it was suggested at a representative meeting of jewelers that a carat should equal .205 of a metric gram, the gram being a convenient weight. The gram represented the exact weight of one cubic centimeter of distilled water at a temperature of 40 Centigrade, and it was a unit already in use in many branches of science.

It is remarkable, however, how many dealers in gem stones can estimate almost correct weights of given stones by eye alone. This applies particularly to brilliants. Daily practice has given them this skill in judgment, the accuracy of which is only exceeded by direct weighing. This skill is of great assistance when one is called upon to value a piece of jewelry which contains a number of various size stones.

Many of the old large diamonds have been known by their weight alone over a great many years, although a universally recognized unit was not always in use. We find various terms describing weights of gem stones in old works, and this has sometimes resulted in confusion. Perhaps the first unit of weight was the small, hard, dried seed of the locust tree, which was found throughout the East and in the Mediterranean countries. The size of this seed was fairly constant, and it was therefore something which could be used as a unit of comparison. In western Europe, the barley seed was used, and a Greek word for the shape of the pods is the derivation of the word carat.

Later, with the almost universal introduction of the metric system of weights and measures, it was realized that a carat equivalent to .200, or one-fifth, of a gram would be far more convenient, and by the year 1913, all dealers had agreed to make this the universal carat. The general adoption has obviated the awkward use of fractions of carats, such as one-eighth and one-sixty-fourth (which were formerly employed), as well as the necessity for dealers to alter the weights of parcels of stones according to the market to which their goods were being dispatched. Also calculations were much simplified when prices or average weights were being considered.

Compared with ordinary weights in common use, a carat is small. A round diamond, proportionately cut and weighing one carat, would be the size of the illustration shown. Other gem stones would be slightly larger or smaller, according to how their specific gravities compare with that of diamond. This size, and others, can be memorized by the constant examination and handling o£ stones, and it is very useful for the dealer to keep such sizes in mind for the purposes of comparison.

When the carat is not used as the unit weight, Troy weights are used in England, and the metric system of grams and kilograms (1 kilo, equals 1,000 grams) in the U.S.A. and on the Continent. But the carat is used in connection with nearly all stones. With rough stones of small value, such as opal, amethyst, and turquoise, Troy ounces are used. Rough amber is bought by the kilogram or ounce Troy, coral by the gram, while such bulky material as rock crystal is bought in the rough by the hundredweight (avoirdupois) or kilogram.
The relative weights of the carat are 1 carat equals .200 gram, or one-fifth of a gram,

or, 3.08647 grains Troy,
or, .00705478 ounces Avoirdupois