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Outstanding fine stones, being so rare, have no fixed price. Various rules for the valuation of gem stones have been devised, but owing to varying prices through current demand, these rules cannot be followed with safety. Only those in the market can judge the current value of stones. David Jeffries, in his Treatise on Diamonds and Pearls, published in 1750, laid down a formula by which diamonds could be priced, and others have, in later years, tried to produce a similar ready made guide. Sutton, an authority on diamond, gives a formula which is considered by many to give good results over a wide range of sizes, but no reliable figures can be given.

It should be mentioned again that the economic state of a country has a great influence on the price of gems. If conditions are peaceful and prosperous, there is a good and steady demand, and prices do not fluctuate greatly. For instance, during a period before the French Revolution, European courts and certain strata of society showed great extravagance, and the values of all precious stones increased. But during the Revolution and in the succeeding years, they fell again.

From 1801 to 1872, diamond regained its pre-eminence, since when the emerald has become the most expensive stone. It may be said that, in the past 150 years, the price of ruby has increased about six times its original value, sapphire fifteen times, diamond twenty-five times, and emerald thirty times, which proves that ruby must have been regarded as the most precious stone in the Eighteenth Century.

Good colored rubies of over four carats in weight, white diamonds of unusual size and brilliancy, emeralds of deep color, and large fine sapphires all realize exceptionally high prices if they are flawless. Such prices do not keep to any rule any more than does a unique picture. Actually, very fine rubies of over about five carats in weight are the rarest of all stones, and they realize up to $5,600 or £2,000 per carat, but a flawless perfect emerald is a greater rarity and therefore reaches a higher price. Both fine emeralds and rubies are now seldom found since the old mines are either closed or exhausted. The Cashmere mines which have produced the finest sapphires are also not worked.

There are some stones which have a greater value in some localities than in others. For instance, in America we have the locally mined benitoite, kunzite, hiddenite, and tourmaline, and these are more in local demand than elsewhere. Chinese jade in China, star stones in the East, and turquoise in Persia and Tibet (turquoise beads are current in Tibet as small change in the payment of taxes) all find a better price than they do elsewhere. Tourmalines were not recognized in Europe until they were found, in the year 1703, among a parcel of assorted Ceylon stones discarded by a Dutch lapidary. Yet they were used and valued in the East long before that date.