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A gemstone is prized especially for great beauty or perfection. Hence, appearance is almost the most important attribute of gemstones. Characteristics that make a stone beautiful or desirable are colour, unusual optical phenomena within the stone, an interesting inclusion such as a fossil, rarity, and sometimes the form of the natural crystal. In terms of beauty, it is unsurprising that diamond is prized highly as a gemstone, since it is the hardest substance known and is able to reflect light with fire and sparkle when faceted. However, it is important to understand that diamonds are far from rare with millions of carats mined each year.
Traditionally, common gemstones were classified into precious stones (cardinal gems) and semi-precious stones. The former category was largely determined by a history of ecclesiastical, devotional or ceremonial use and rarity imposed by the limits of known deposits and available collection methods. Only five types of gemstones were considered precious: diamoind, ruby, sapphire, emerald and amethyst.
In current usage by gemologists, all gems are considered precious, although four of the five original "cardinal gems" are usually?but not always?the most valuable.
Another category of gemstones which is still in use is that of rare or unusual gemstones, generally meant to include those gemstones which occur so infrequently in gem quality that they are scarcely known except to connoisseurs. Here are included andalusite, axinite, cassiterite, clinohumite, iolite, among others all of which are durable, rare, and in better examples quite attractive.
The factors influencing the esteem in which gems are held are few in number but extremely important because they so directly affect value. These are attractiveness, durability, rarity, fashion, and size. They are not fixed in scope by any means and the predominance of one factor may compensate for shortcomings in another.
Some gemstones are manufactured to imitate other gemstones. For example, cubic zirconia is a synthetic diamond simulant composed of zirconium oxide. The imitations copy the look and colour of the real stone but possess neither their chemical nor physical characteristics.
However, true synthetic gemstones are not necessarily imitation. For example, diamonds, ruby, sapphires ad emeralds have been manufactured in labs, which possess very nearly identical chemical and physical characteristics to the genuine article.
Synthetic corundums, including ruby and sapphire, are very common and they cost only a fraction of the natural stones. Smaller synthetic diamonds have been manufactured in large quantities as industrial abrasives for many years. Only recently, larger synthetic diamonds of gemstone quality, especially of the coloured variety, have been manufactured.
Always remember, certain material or flaws within a stone may be present as characteristic inclusions. And the gem may occur in certain locations, "occurrence." Gems from different locations may display different characteristics which may aid in identification.
Other guides relating to jewelry and gemstone buying which you may find helpful are as follows:
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