Precious stones range high in the world's annual production of mineral values. A hundred or more minerals are used to some degree as precious stones; but those most prized, representing upwards of 90 per cent of the total production value, are diamond, pearl, ruby, sapphire, and emerald. In total value the diamonds have an overwhelming dominance. Over a ton of diamonds is mined annually. Diamonds come mainly from South Africa, which produces over 99 per cent of the total. Pearls come chiefly from the Indian and Pacific oceans. Burma is the principal source of fine rubies. Siam is the principal producer of sapphires. Colombia is the principal source of fine emeralds. The United States produces small amounts of sapphires (in Montana) and pearls (from fresh-water molluscs). Diamonds, rubies, and emeralds are practically absent on a commercial scale. Of other precious and semi-precious gem stones produced in the United States, the principal ones are quartz, tourmaline, and turquoise. On the other hand, the United States absorbs by purchase over half of the world's production of precious stones. It is estimated roughly that there are now in the United States nearly one billion dollars' worth of diamonds, or over one-half of the world's accumulated stock, and probably the proportions for the other stones are not far different. Value attaches to a precious stone because of its qualities of beauty, coupled with endurance and rarity, or because of some combination of these features which has caught the popular fancy. No one of these qualities is sufficient to make a stone highly prized; neither does the possession of all of them insure value. Some beautiful and enduring stones are so rare that they are known only to collectors and have no standard market value. Others fail to catch the popular fancy for reasons not obvious to the layman. While the intrinsic qualities go far in determining the desirability of a stone, it is clear that whim and chance have been no small factors in determining the demand or lack of demand for some stones. As in other minerals, value has both its intrinsic and extrinsic elements. For the leading precious stones above named, the values are more nearly standard throughout the world than for any other minerals, with the exception of gold and possibly platinum. Highly prized everywhere and easily transported, the price levels show comparatively little variation over the world when allowance is made for exchange and taxes. The valuation of precious stones is a highly specialized art, involving the appraisal not only of intrinsic qualities, but of the appeal which the stone will make to the buying public. In marking a sale price for some exceptional stone not commonly handled in the trade, experts in different parts of the world often reach an almost uncanny uniformity of opinion.