The traditional classification in the West, which goes back to the Ancient Greeks, begins with a distinction between precious and semi-precious; similar distinctions are made in other cultures. In modern usage the precious stones are diamond, ruby, sapphire and emerald, with all other gemstones being semi-precious. This distinction reflects the rarity of the respective stones in ancient times, as well as their quality: all are translucent with fine color in their purest forms, except for the colorless diamond, and very hard, with hardnesses of 8 to 10 on the Mohs scale.
Other stones are classified by their color, translucency and hardness. The traditional distinction does not necessarily reflect modern values, for example, while garnets are relatively inexpensive, a green garnet called Tsavorite, can be far more valuable than a mid-quality emerald. Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone. Use of the terms 'precious' and 'semi-precious' in a commercial context is, arguably, misleading in that it deceptively implies certain stones are intrinsically more valuable than others, which is not the case.
Aside from the diamond, the ruby, sapphire, emerald, pearl and opal have also been considered to be precious. Up to the discoveries of bulk amethyst in Brazil in the 19th century, amethyst was considered a precious stone as well, going back to ancient Greece. Even in the last century certain stones such as aquamarine, peridot and cat's eye (cymophane) have been popular and hence been regarded as precious.
Nowadays such a distinction is no longer made by the gemstone trade. Many gemstones are used in even the most expensive jewelry, depending on the brand name of the designer, fashion trends, market supply, treatments, etc. Nevertheless, diamonds, rubies, sapphires, and emeralds still have a reputation that exceeds those of other gemstones.
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, include andalusite, axinite, cassiterite, clinohumite and red beryl.
The world of precious gemstones is endlessly fascinating, for centuries, nearly every culture has held the belief that precious gemstones possess magical characters or the ability to provide the wearer with some properties. Often people don't have the time for physically visiting the store and purchasing the jewelry. And they would like to do it virtually through the online shopping.
One of the main advantages of buying gems online is that the expense can be incredibly reduced than buying it directly from the store. Most of the gem stores online offer lower overhead costs and thus the savings would reach the customers. Another advantage is that you don't have to waste your time and money traveling from one store to another. Every gem production would be only a few pressure of your mouth.
Above all, the precious gemstones that you purchase should be worth the money. The precious gemstone is expected to last for a life time and sometimes they may be carried down the generations even. So the quality of the gems is essentially important.