Gemstones can be measured by weight, size or both. The basic unit for weighing gemstones is the carat (with a C), which is equal to one-fifth of a gram. Carats are divided into 100 smaller units, called points. For example, a half-carat gemstone would weigh .50 carats or 50 points. When gemstones are measured by dimensions, the size is expressed in millimeters (for example, 7x5 mm.). Many gemstones are treated in some manner to improve their appearance or durability, or even change their color. Jewelers should tell you whether the gemstone you are considering has been treated since it may affect its value or require some special care.

Diamonds, the proverbial girls' best friend, are valued on four basic criteria: color, clarity, cut, and carat. The color of a diamond is usually "graded" on a scale. However, scales are not uniform: a "D" may be the best color on one scale, but not for another. Clarity refers to the presence or absence of internal flaws, called inclusions, which occur naturally within the stone, or to external blemishes, such as scratches or chips. A diamond can be described as "flawless" only if it has no visible surface or internal imperfections when viewed under a 10-power magnification by a skilled diamond grader. Make sure you know how a particular scale and grade represent the color or clarity of the diamond you are considering. Cut refers not only to the shape of the diamond, but also to size, angle, uniformity and polish of the facets (faces of the stone). Carat weight may be described in decimal or fractional parts of a carat, as described above.

Imitation diamonds, such as cubic zirconia, resemble diamonds in appearance but are much less costly since they are made in a laboratory. Other synthetics such as lab-created moissanite, also resemble diamonds and may not be detected by the instruments used to identify cubic zirconia. Ask your jeweler if he has the latest testing equipment to distinguish between real diamonds and lab-created stones.

Natural or "real" pearls are made by oysters and other mollusks. Cultured pearls are also grown by mollusks, but with human assistance: that is, an irritant introduced into the shells causes a pearl to grow. Imitation pearls are completely man-made using glass, plastic or organic materials. Because natural pearls are very rare, most pearls used in jewelry are either cultured or imitation. Cultured pearls, because they are produced by mollusks, are usually more expensive that imitation pearls. A pearl's value is largely based on size, usually state in millimeters, and the quality of its nacre coating, which gives it luster. Jewelers should tell you whether a pearl is imitation or cultured.

Some black, bronze, gold purple, blue and orange pearls, whether natural or cultured, occur that way in nature. Some, however, are dyed through various processes and jewelers should tell you whether the colored pearls are naturally colored, dyed or irradiated.

When you're in the market for a piece of jewelry for yourself or someone you love, shop around. Whether it is online, in catalogs or at a traditional store make comparisons. Compare quality, price, and service. Ask about refund and return policies before you buy. Check for the appropriate markings on metal jewelry. And make sure you get a sales receipt containing any information you relied on when making your purchase.

Best wishes for an enjoyable and rewarding shopping experience!