Gemstone Buying Guide

There is no scientific or geological definition for ''gem'' or ''jewel''; these are human concepts. Minerals are formed by geological processes which happen continuously deep inside the Earth. When people excavate certain minerals and cut them into specific shapes, they become gems. When placed in a decorative setting for wearing, they become jewels. Factors determining the value of any gem or jewel are rarity, durability, beauty, size and color.

The geological processes create an astonishing variety of beautiful gemstones. Only a few are ready for jewelry in their natural state, so, many companies treat their stones to enhance their color and brilliance or stabilize their chemical composition, making more high-quality gems available to the public. It has been estimated that 80-percent of all gemstones are treated in some way before reaching the retailer. Every jewelry description at Overstock.com includes gemstone treatment codes; you can visit Overstock.com's Gemstone Treatment Guide and know exactly what you're getting before you buy.

Gemstone buying tips

Colored gemstones, like diamonds, are classified and evaluated by the ''Four Cs'': color, carat weight, cut and clarity.

Color
The most important factor in evaluating gemstones; those with the brightest, most vivid colors usually command the highest price. Specific gemstones only occur in certain color ranges, based on their chemistry. When evaluating color (and all other factors, for that matter), evaluate each stone against others of its kind. For example, you can't call a peridot a weak green just because it isn't the same green as an emerald.

Carat Weight
Heavier gems are more rare and expensive than smaller ones; in fact, there's no bulk discount in gemstones--for every $1.00 per carat a small stone might cost, a larger stone might be $1.25, $1.50 or more per carat. Rarity of large stones also depends on the type: The world's largest cut ruby is just over 23ct, while the largest cut topaz is just under 23,000ct! Carat measures the stone's weight, but the crystal structural and other chemical properties can affect density, meaning two stones of the same size may have different weights. For this reason, colored gemstones are often listed by size instead of weight. (By the way, 'carat' measures weight; 'karat' measures gold's purity--24k is 100-percent gold.)

Cut
Determining the final beauty of a stone means picking precise angles and proportions. Diamond cutting focuses on maximizing brilliance (reflected light), while in colored gemstones, it's about maximizing color. There are many traditional cuts--round brilliant, oval, emerald, square, princess, cabochon, pear, marquise--and jewelers continue to look for better ways to show off their gems. A quality cut can be the difference between a good stone and one that is breathtaking.

Clarity
Describes the ''inclusions'' or flaws existing in all natural stones--it's part of the proof of their natural origin. Fewer flaws mean a more valuable stone. Inclusions can also help determine if a gemstone has been treated. As with other factors, clarity is related to type. Some gems usually occur with few or no inclusions, while others are known for them--a flawless emerald would be nearly priceless while flawless aquamarines are fairly common. As with diamonds, 10x magnification and a well-trained eye are used by gemologists to evaluate clarity.

The jewelry industry is heavily regulated to prevent misrepresentation or fraud. By law, every object must be clearly and obviously described as to gem type, cut, weight, etc., following regulations set down by the US Federal Trade Commission. All jewelry sold at Overstock.com conforms to these regulations.

Gemstone care

Avoid wearing fine jewelry in activities that could damage them--yard work, sports or around harsh chemicals. The best way to clean fashion jewelry is a warm water rinse. If needed, gently scrub the stones with a soft brush, like a toothbrush. Rinse thoroughly and lay on a soft cloth to dry. Opaque gemstones like lapis lazuli, turquoise and malachite should just be wiped clean with a moist cloth. These gems can be porous and may absorb soap or chemicals, which can discolor them.

Visit your jeweler at least once a year to have your jewelry professionally cleaned. The jeweler can also check the settings to make sure prongs haven't been bent or weakened. You'll find that clean stones heighten the sparkle of your jewelry.

Of course, Overstock.com features numerous jewelry boxes in a variety of sizes and styles, all of which are designed to protect your investment.

Artificial gemstones

"Not all that glitters is gold" wrote J. R. R. Tolkein; he might have added, ''Not all that sparkles is a gem.'' Imitations of various qualities and costs are available, and consumers should not pay for what they are not getting. The FTC defines two types of non-natural gems:

"Lab-created…has the same chemical, physical, and optical properties of the natural ruby, emerald, diamond, etc." Minerals have a specific composition which can be duplicated; these are real rubies, sapphires, etc., in every sense--identical to natural gemstones the way cultured pearls are identical to natural pearls. Natural stones have inclusions or flaws because of impurities in the rocks in which they formed, lab-created gems have few, if any. Some people think this should make them more valuable, but the fact that they are not natural, combined with the lower cost of production, makes some lab-created gemstones far more affordable than natural stones.

"Simulant (or imitation) merely resembles the natural stone" Crystals that look like gems but do not share the same composition are simulants. For example, a diamond is pure carbon; a lab-created diamond is also pure carbon. A cubic zirconia (CZ) is zirconium oxide. CZs can look so diamond-like that only an experienced jeweler can tell the difference--in the stone, that is, anyone can tell a diamond from a CZ by looking at the price tag. There are numerous types of simulated gems, each with characteristics that set it apart from real gemstones. These faux treasures look real, are more affordable than real gems and are perfectly acceptable to wear in any jewelry.

Overstock.com sells many artificial, very affordably-priced, gemstones; every one clearly identified as imitation, simulated, faux, lab-created or some other recognizable description.