Value of natural pearls
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.