Carat—the standard unit of weight.
The word carat derives from carob seeds because early gemstone appraisers used carob seeds as counterweights on their scales.
One carat weighs 0.2 grams, and one carat is equal to 100 points. Therefore, a quarter carat weighs 25 points, a half carat weighs 50 points and a three-quarter carat weighs 75 points. It takes about 142 carats to equal one ounce.
A fraction of a carat can mean a big difference in the value of a diamond, so precision in measuring is crucial. Carat weight is often measured to the hundred thousandths of a carat, and rounded to a hundredth of a carat.
Note: Diamond carat should not be confused with gold karat, which refers to gold purity.
Color—colorless is more valuable.
Diamonds are valued by how closely they approach colorlessness: the less color a diamond has, the higher its value. The exception to this rule are the rare colored diamonds—known as “fancy” colored diamonds—which are growing in popularity. Most diamonds sold in retail stores are near colorless to faint or light brown or yellow.
The Gemological Institute of America’s universal color scale starts at D, representing colorless, and goes through Z and beyond to the fancy and vivid colors. The higher the letter, the more presence of color in the diamond.
Clarity—a diamond’s internal and external flaws
Blemishes are external flaws, and inclusions are internal flaws. Inclusions are created when the diamond is formed, or when the diamond is cut. Because 100 percent “perfect” diamonds are very rare in nature, those with fewer blemishes and inclusions are rarer and cost more.
The GIA International Diamond Grading System™ Clarity Scale is the standard clarity grade scale, and contains 11 grades. Diamonds are assigned a clarity grade ranging from flawless (FL) to diamonds with obvious inclusions (I3). Most diamonds are graded in the VS (very slightly included) or SI (slightly included) categories.
To determine a diamond’s clarity, appraisers using the GIA Clarity Scale consider different variables, including the diamond’s size, nature, position, color or relief, and quantity of clarity characteristics visible under 10X magnification.
Cut—rates characteristics of shape.
The GIA system rates a diamond’s cut using five grades: Excellent, Very Good, Good, Fair, and Poor. The system considers factors such as brightness, fire and scintillation, weight ratio, durability, polish, and symmetry.
The cut of any diamond has three attributes: brilliance (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), and scintillation (the flashes of light, or sparkle, when a diamond is moved).
Most diamond jewelry uses the standard round brilliant shape. All others are known as fancy shapes, and include the marquise, pear, oval, and emerald cuts. Diamond shapes such as hearts and triangles are also gaining in popularity.
Understanding the cut, color, clarity, and carat of a diamond is important, but when it comes down to it, choosing the right diamond is also subjective: how you feel and what you like. Don’t just focus on the GIA rating—go with a diamond that looks beautiful to you—or better yet, your mate will appreciate—and is in your budget. Make sure you know the person’s taste and ring size, as well as the jewelry store’s return policy.