flaws within a diamond caused during its formation. External marks are known as blemishes, while internal ones are called inclusions. Diamonds are graded for clarity on a scale ranging from "F" for flawless (no blemishes or inclusions visible under 10x magnification) to "I" for imperfect (inclusions visible to the naked eye), with numerous grades and subgrades in between. The best diamonds, of course, are flawless, but these stones are exceptionally rare and therefore very costly.

Carat weight refers to the size of the stone. The carat is the measure of weight for diamonds. One carat is approximately 200 milligrams, or 100 "points". A stone weighing a half-carat would be a 50 pointer, and so on. In general, larger diamonds are rarer and have a higher value per carat. However, other factors such as cut, color and clarity come into play as well in determining a stone's value. It's entirely possible for a smaller stone of exceptional cut, color and clarity to be worth more than a larger stone of only average quality in these areas.

There are even fancy natural colored diamonds in reds, pinks, blues, greens, yellows, browns and other colors. They vary in color richness or saturation from "faint" to "vivid", with the latter grade reserved for stones with the most vivid and deepest saturation. The value of a fancy stone depends largely on the rarity of its color (for instance, reds and greens are rarer than yellows

and browns); the saturation of the color; and the purity of the color (whether the color is bright and clear or clouded by tinges of other underlying colors). Top grade fancy diamonds are extremely rare and can command tremendous prices. Probably the most famous colored diamond is the Hope, a 45.52-carat deep blue gem that resides in the Smithsonian Institution in Washington, D.C.

Even though diamonds are the hardest known substance on earth, rating a "10" on the Mohs scale of hardness, they can still be damaged if they aren't handled with care. Since only diamonds can scratch other diamonds, it's important to wrap and store your diamond jewelry pieces separately so they aren't touching one another. Also, diamond jewelry should never be worn during heavy work, since points are vulnerable to chipping and the setting can be loosened. Visit a jewelry retailer every six months to have your diamonds, mountings and settings checked.

As for cleaning, it's always best to have this done by a professional. To clean jewelry at home, you can soak your diamonds in warm, sudsy water made with any mild liquid detergent, brush with a soft toothbrush, then rinse and pat dry with a soft, lint-free cloth. Other effective cleaning methods include soaking diamonds in household ammonia, brand-name liquid jewelry cleaners and even a glass of vodka.