A diamond ring is no frivolous purchase. Before you hand over your hard-earned cash for some flashy bling, it's important to know how diamonds are classified in terms of quality. A diamond's rating in four major categories (cut, clarity, color and carats   collectively known as the 4 C's) determines the overall quality and thus cost of a diamond. Whether you're shopping local jewelry stores for an engagement ring or browsing online jewelry stores for a loose stone, here is everything you need to know about the all-important 4 C's.

Carats   Arguably the most well-known characteristic of the 4 C's is carat weight. Carats refer specifically to a gemstone or pearl's weight, not necessarily its size, as many people mistakenly believe. One carat is equivalent to 200 milligrams, so a 2-carat diamond weighs approximately 400 milligrams or 0.4 grams. A diamond's carat weight should not be confused with the similar sounding karat, which refers to the purity of the precious metal gold. The more carats a diamond has, the rarer and typically more expensive the diamond.

Clarity   Diamonds are created deep beneath the Earth's surface under extreme pressure and heat. During formation, the stones can sustain slight imperfections. These imperfections are known as inclusions inside the diamond, and blemishes on the surface of the diamond. Clarity simply refers to the degree in which these flaws are present or visible.

Most diamonds are graded for clarity using the Gemological Institute of America's (GIA) 11-point grading scale. Under this scale, the GIA uses 10x magnification to consider the number, size, color, reflectivity and position of every visible flaw. The scale ranges from flawless (FL), which means no inclusions or blemishes are visible under magnification, to I1 through I3, which means inclusions are obvious under magnification and likely to affect the transparency and brilliance of the stone.

Color   You may not know it, but diamonds come in a wide range of colors. However, most people are interested in white or colorless stones. Many diamonds have a tint of yellow, some more obvious than others. This can affect the value of the diamond and, conversely, the more white or less color in a diamond, the greater its value.

The GIA grades diamond color on a scale of D (colorless) to Z (light, visible color). This grading scale is not applicable to true colored diamonds, such as pink diamonds; they are graded on a separate color scale.

Cut   Many people think a diamond's cut refers to its shape (e.g., round, oval, etc.). Cut actually concerns the proportions, symmetry and reflective qualities of a diamond. The brilliance of a diamond depends more on the cut than any other characteristic; if a diamond is cut poorly, its luminosity (think its sparkle or shine) is diminished.

When a diamond is cut with what gemologists consider ideal proportions, light reflects out of the top of the stone, allowing for optimal brilliance. If the stone is cut too shallow, the light seeps out of the bottom of the stone, while a too-deep cut allows light to escape from the sides. The GIA's grading scale for diamond cut ranges from excellent to poor; diamonds rated excellent have superior light performance, while diamonds rated poor or fair lack brilliance and don't have very much shine.

The Bonus C: Certification   Some brick-and-mortar and online jewelers consider certification to be the fifth C of diamonds. This means that any diamond you are considering is accompanied by a diamond certificate or grading report. This is a quality certification issued by an independent gem laboratory, such as the GIA, and it verifies the authenticity and characteristics (the 4 C's) of the stone.

No matter what type of diamond jewelry you are looking for, it is imperative that you understand the 4 (and sometimes 5) C's of diamonds. This knowledge will allow you to properly evaluate gemstone quality and make your diamond purchase with confidence.

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