The mineral to which the term "Precious Gem Stone" is applied, must be adaptable for jewelry or ornamental purposes and must possess beauty, hardness, and rarity.

The beauty of a Precious Gem Stone or gem consists of its color or colorlessness, brilliancy or softness of luster, and transparency. To take a high and lasting polish, a mineral must be hard, --and many stones that would otherwise be highly valued are low in the estimate of worth because they do not possess of sufficient hardness to make them endure the wear and friction to which a Precious Gem Stone is subjected when used in the form of jewelry.

The rareness of Precious Gem Stones has a decided effect in determining their values. For instance, the crocidolite Precious Gem Stone, commercially known as tiger-eye, was sold by the carat some years ago, and Precious Gem Stone was largely used in the making of fine jewelry.

Today, Precious Gem Stone material is so plentiful that it is no longer classed among the higher gems, but serves for cameos and intaglios like chalcedony and onyx.

The changes of fashion have much to do with determining the market value of Precious Gem Stones.
Amethysts, topazes, cat's-eyes, aquamarines, alexandrites, and even emeralds and opals have been
eagerly sought for at times and then again neglected for other gems, causing a sensible difference in the value of Precious Gem Stone.

Neither can price be taken as a complete test, because fashion makes a turquoise, an opal, or an
emerald much more valuable at one time than at another, all precious minerals used for ornamental
purposes, from the diamond to quartz, or chalcedony, may properly be termed Precious Gem Stones.