Composed of carbon and formed by heat and pressure deep underground, diamonds often star in engagement rings and fine jewelry. In the 1940s, the Gemological Institute of America (GIA) developed a grading system to compare diamonds.
Carat
A carat is a universally accepted metric weight for gemstones. To ensure accuracy, the standard is to measure the weight of a diamond to the hundred-thousandths of a carat. Although diamonds may have the same carat weight, their values will differ based on their individual color, clarity and cut.
Color
The less color a diamond has the higher its value. This rule, however, does not apply to fancy-colored diamonds that are pink or blue. The GIA color-grading scale rates diamonds from D, colorless, to Z, near-colorless.
Clarity
The presence or absence of inclusions and blemishes as well as their size, location and color determine a diamond's clarity. The GIA clarity scale is made up of 11 designations that range from flawless to included, those with obvious inclusions.
Cut
While difficult to measure, a diamond's cut is the amount of light the diamond reflects and how the diamond disperses light and sparkles. The proportions, symmetry, polish and shape of a diamond all affect its cut.
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