Despite the immense popularity of diamonds, colored gemstones have always been among the most popular and expressive forms of jewelry. The bright colors of colored gems give each a unique personality, and personal tastes in color often dictate preferences for particular stones.

Long before diamonds were found worthy of jewelry, people revered sapphires, rubies, emeralds, and all manner of colored stones. In addition, almost all colored gems were believed to have special powers or cure specific illnesses. There was a time when a collection of different gemstones was the equivalent of a medicine cabinet!

Today, gemstones are still loved for their beauty and "personality." The precious gemstones - sapphire, ruby, and emerald - are among the most prized. Precious gemstones of good size and quality are so rare that a natural, unenhanced, strongly colored stone can be worth as much per carat, or more, than a diamond of comparable quality.

Given the extreme cost and rarity of such stones, jewelers developed ways to enhance the appearance of more common stones, both precious and semi-precious. For hundreds of years, it has been common practice to heat gems to bring out their best color. This is viewed as simply extending what nature started, since it is the heat and pressure within the earth that gives gems their color.

There are many other common types of treatment to enhance the beauty of colored gemstones. Emeralds are often oiled and waxed to protect them and to hide fine lines that naturally occur in the stone. Some sapphires have their blue color enhanced using diffusion, a chemical process. Certain stones are treated with radiation, again mimicking the processes of nature. All these practices are standard in the jewelry industry; in fact, enhancement is so common that good quality unenhanced stones often come with a certificate stating that fact.

Other than the oil on emeralds, which can last for years before needing replacement, any quality enhancement is permanent and should not require special care. With emeralds, you should simply be careful not to clean the stone too vigorously or you might remove the layer of wax or oil, changing the appearance of the stone. If this happens, bring it to your jeweler to have the layer reapplied. Bringing your emerald in for a cleaning and re-oiling on a regular basis will help keep it looking its best.

Synthetic or "lab-created" stones, on the other hand, are grown using the same ingredients as the natural stones. They are chemically identical to natural stones, but more affordable, and its easier to get a large, well-colored lab-created gem than a natural one. Lab-created gems frequently have fewer "inclusions," the internal flaws common in precious gems. With technical advances, many high quality lab-created stones can only be differentiated from a natural by a trained professional. Almost any gem can be made in a lab, but the precious gems - emeralds, rubies and sapphires - are the most common.

Included in each gemstone description below is its Mohs' Hardness Rating, based on the system developed by Austrian mineralogist Friedrich Mohs to compare the relative hardness of different minerals. The scale ranks from softest (talc, with a ranking of 1) to hardest (diamond, which is the only mineral ranked 10). Hardness is the resistance to scratching. When various minerals are scratched against each other, any mineral with a higher hardness ranking will mark any mineral with a lower ranking.

PRECIOUS GEMSTONES: Only three colored gemstones are considered precious. These are the emerald, sapphire and ruby, which have retained their prized positions among jewels due to their extraordinary colors and extreme rarity. Precious gemstones with good color and large size are very hard to come by. Because of their rarity, it is common to use stones with inclusions and blemishes in jewelry.

SEMI-PRECIOUS GEMSTONES: A semi-precious gemstone includes any gemstone other than sapphire, emerald or ruby. The value of semi-precious gemstones can vary depending on the availability of the mineral; natural black opal, for example, is hard to come by and more valuable than most other semi-precious stones. As a rule, however, semi-precious stones are always more plentiful than precious stones. That makes it easier to find large, well-colored, very clean stones appropriate for jewelry. In addition, the wide range of colors available makes semi-precious stones the choice for people who want to create their own look with their jewelry.