are so valuable, its essential to have a universal grading system for comparing their quality. That's why in the 1940's GIA developed the 4C's and the Internet Diamond Grading System to objectively compare and evaluate diamonds.
Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip. (Dont confuse carat with karat, as in 18K gold, which refers to gold purity.) Just as a dollar is divided into 100 pennies, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other members of the Four Cs: clarity, color and cut. The majority of diamonds used in fine jewelry weigh one carat or less.
Diamond color is all about what you cant see. Diamonds are valued by how closely they approach colorlessness the less color, the higher their value. (The exception to this is fancy-color diamonds, such as pinks and blues, which lie outside this color range.) The color-grading scale for diamonds begins with the letter D, representing colorless, and continues with increasing presence of color to the letter Z, or near-colorless. Each letter grade has a clearly defined range of color appearance. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.
Because diamonds formed deep within the earth, under extreme heat and pressure, they often contain unique birthmarks, either internal (inclusions) or external (blemishes). Diamond clarity refers to the absence of these inclusions and blemishes. Diamonds without these birthmarks are rare, and rarity affects a diamond's value. Using the GIA International Diamond Grading System™, diamonds are assigned a clarity grade that ranges from flawless (FL) to diamonds with obvious inclusions (I3).
Cut is the factor that fuels a diamonds fire, sparkle and brilliance. The traditional 58 facets in a round brilliant diamond, each precisely cut and defined, are as small as two millimeters in diameter. But without this precision, a diamond wouldn't be nearly as beautiful. The allure of a particular diamond depends more on cut than anything else.