Mineral Guide > Gems


GemsGems are minerals prized for their color, hardness, luster, and, for the most part, transparency. It is generally essential that a mineral to be a gem should excel in at least three of the above-named properties, although a few are superior in only two.

Some minerals may, for example, possess desirable color and luster, but, lacking hardness, are little used for gem purposes, because they would become quickly marred when worn. Fluor-spar is an illustration of such a mineral.

That a high degree of hardness is not essential, however, to the employment of a mineral as a gem is shown by the extensive use of such substances as pearl, amber, jet, and turquois, for gems. All of these are easily scratched by ordinary objects. It is to be noted, however, that they are not transparent substances, and that an opaque or translucent substance may endure, without serious injury, scratches which would be fatal to the beauty of a transparent gem.

Hardness and color alone cannot, however, make a mineral suitable for gem purposes. This fact is illustrated by many varieties of corundum, which have a high degree of hardness and good body color, but are not used for gems because not transparent. It is evident, therefore, that no fixed rule can be assigned for the use of a mineral as a gem, the favor or disfavor in which it is held seeming, in many instances, to be a matter of pure caprice.

But, however capricious popular favor may seem to be in its estimate of the qualities desirable in gems, it may be set down as a fairly general rule, that the gems which combine the most of the qualities previously mentioned are those most highly prized. Thus, a red or blue diamond, excelling as it does all other minerals in hardness and luster, and being the equal of any in color and transparency, is the most valuable of gems. The ruby and sapphire excel in hardness, and have good color, luster, and transparency. They rank among the most valuable of gems.

In speaking of minerals which have desirable gem qualities, it must not be supposed that this includes all occurrences of any particular mineral species. On the contrary, only selected portions usually have the desired qualities. A large part of the yield, even of diamond, is of no value for gem purposes, though it all finds commercial use on account of its hardness. Quartz, one of the most abundant minerals of the earth's crust, though it has the qualities of hardness and luster suitable for a gem, can be used only in small quantity comparatively for gem purposes, since only few pieces have the desirable color and transparency.

The selection of stones which bear the qualities above mentioned for purposes of possession and ornament seems to be a taste as old as the human race itself. In the oldest Egyptian tombs are to be found necklaces containing emeralds, garnets, carnelians, and other precious stones. The history of many gems of India dates from a period so remote as to be indeterminate. The desire to obtain amber led the Phoenicians to make some of their earliest and longest voyages. Gems were wrought into the earliest ritual of the Hebrews, and allusions to them are frequent throughout their Scriptures.

The ancient Arabs were familiar with many of the gems used at the present day, and ascribed to them special qualities. The Persian turquois mines are known to have been worked as far back as 1300 A. D., and probably much earlier. There is frequent mention of gems by Greek writers, and the Romans, especially in the later days of the Empire, seem to have had great fondness for jewels, and to have sought them eagerly in their conquests. They used them in great variety and abundance, and carried the art of cutting and engraving them to a high degree of perfection.

Moreover, gems are wrought into the history and literature of nearly all peoples, and furnish standards of color, hardness, luster, etc., which pass current the world over. Such terms as the " emerald meadow," " turquois sky," "adamantine hardness," etc., are derived from the use of gems, and have universal significance. Advances in civilization seem to increase rather than diminish the number of minerals used as gems, the number now employed being larger than ever before in the world's history.

While it is true that the qualities which have been prized in gems, and the relative esteem in which they have been held, seem to have been much the same in all ages, the fashion in gems may vary from time to time, so that now one stone and now another may take on temporarily a higher value. Yet, on the whole, their worth varies little among different peoples and at different times. The principal exception to this rule is found in the valuation of jade by the Chinese, for they esteem this above all other precious stones. Aside from a few such exceptions, gems pass current in nearly all countries at about the same value.

They hence afford to a certain extent a medium of exchange, and are often made objects of investment, because they are small, portable, and have intrinsic value. It is not likely that any great excess or diminution of supply will occur to change the value of the leading gems, such as diamond, ruby, sapphire, and emerald, as they seem to be distributed in the earth's crust in but sparing amount. Among the less valuable gems, great variations in value have occurred, and may again. Thus the price of precious opal has steadily declined since the discovery of the Australian fields, although as fine gems are produced there as were ever known. Topaz and amethyst have suffered a similar decline in value, while the price of the gem known as "tiger eye" fell in a few years from five dollars a carat to twenty-five cents a pound.

The elements entering into the chemical composition of gems are not as a rule themselves rare. They are chiefly silicon, aluminum, magnesium, and other common elements, usually combined with oxygen, and all abundant constituents of the earth's crust. It is thus not the rarity of their elements which gives gems their high value, but rather their peculiar properties as compounds.

Since gems are unequal in value among themselves, many authorities distinguish between gems and precious stones, and also subdivide the latter into precious and semiprecious. To the class of gems belong, according to such a classification, such stones as the diamond, ruby, sapphire, and emerald; the precious stones include amethyst, rock crystal, garnet, topaz, turquois, moonstone, opal, and the like; and the semi-precious, jasper, agate, carnelian, lapis lazuli, amazon stone, labradorite, etc. Since the different kinds and qualities grade into each other, insensibly however, and no sharp lines can be drawn, the distinction hardly seems worth making. In the following pages, therefore, the terms gem and precious stone will be used interchangeably, and will be considered to include any mineral, and even some substances of animal and vegetable origin, which have attained a certain vogue for purposes of ornament.

Color of Gems
Cutting of Gems
Electrical Properties of Gems
Fluorescence of Gems
Gems by Color
Hardness of Gems
Imitation of Gems
Luster of Gems
Mineral Hardness
Mineral Specific Gravity
Mining of Gems
Mounting of Gems
Phosphorescence of Gems
Price of Gems
Specific Gravity
Superstitions Regarding Gems
Valuation of Gems