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Gemstone Buying Guide

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Stack of dazzling gemstone rings

Although most of us will never see a treasure chest full of emeralds, rubies and sapphires outside a pirate movie, most of us will, at some point, buy or receive gemstone jewelry. This gemstone buying guide presents some basic information to help you recognize and select quality gems for your own collection.

Defining Gemstones:

  1. Geological facts: Gemstones come from the earth and the sea, but there is no scientific or geological definition for ''gem'' or ''jewel''; these are human concepts. When people excavate certain minerals, stones and pearls and cut and polish them into specific shapes, those natural substances become gems. When placed in a decorative fashion jewelry setting for wearing, they become jewels. Rarity, durability, beauty, size and color all contribute to the price of the gemstone.

  2. Organic gems: Organic gemstones are natural substances that are used for jewelry and other decorative arts but are not derived from mineral stones. The term most commonly refers to pearls, amber, coral and jet.

  3. Precious and semiprecious: Historically, rubies, sapphires and emeralds, along with diamonds, were called the precious stones because their rarity made them the most desirable gems among the wealthy. Other popular gems became known as semiprecious, which, unfortunately, hinted that these stones were substandard. As gemstones become more widely available, many of today's jewelers try to avoid these terms. In fact, a high-grade semiprecious stone can be more valuable than a low- or medium-grade precious stone.

  4. Enhancements: Because few gemstones are ready for jewelry in their natural state, they receive treatments to enhance their color and brilliance or to 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 read our gemstone treatment guide and know exactly what you're getting before you buy.

Buying Gemstones:

  1. Quality: Colored gemstones, like diamonds, are classified and evaluated by the "four Cs": color, carat weight, cut and clarity.

  2. Color: Color is the most important factor in evaluating gemstones. Gems 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, compare each stone against others of its kind.

  3. Carat weight: Gemologists measure gemstone weight in carats; 1 carat equals 200 milligrams. Heavier gems are more expensive than lighter ones, but what is considered to be a large stone varies according to type. For example, the world's largest cut ruby weighs just over 23 carats, while the largest cut topaz weighs just less than 23,000 carats. Carat measures the stone's weight, but crystal structure and other chemical properties can affect density, meaning two stones of the same size may have different weights. For this reason, product descriptions often list colored gemstones by size instead of weight.

  4. Cut: The cut of a gemstone determines the final beauty of the stone. Cutting a gemstone is not as specific as cutting a diamond. Diamond cutting focuses on maximizing brilliance, or reflected light. Cutting a gemstone properly is all about maximizing color. There are many traditional cuts, including round brilliant, oval, emerald, square, princess, cabochon, pear and marquise. Jewelers continue to look for new ways to show off their gems. A quality cut can be the difference between a good stone and a breathtaking gem.

  5. Clarity: Clarity describes the inclusions, or flaws, existing in all natural stones. 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, for example, would be nearly priceless, but flawless aquamarines are fairly common. Gemologists use 10x magnification and a well-trained eye to evaluate gemstone clarity.

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