The value of a diamond differs widely from one stone to another. Experts evaluate every diamond for rarity and beauty using four primary guidelines called The Four C's: cut, color, clarity and carat weight.

Cut

When referring to the cut, many people may think of the shape of the diamond. The most popular shapes include Round, Oval, Square, Princess, Emerald, Baquette, and Marquise cuts. Many specialty shapes are also available.

While cut does refer to shape, it also refers to the proportions of how the diamond is actually cut. Diamonds are cut into many different shapes, reflecting not only popular taste but the proportions and quality of the rough diamond. A diamond's overall proportions, as well as the size and placement of its many reflective surfaces or facets, also play a large part in "cut," which determines the diamond’s sparkle. The consistency and balance of these can greatly affect how the stone captures light and reflects it back to the eye.

Color

With some exceptions, the most valuable diamonds are those with the least color. The color scale for transparent diamonds runs from D-F (colorless), G-J (near colorless), K-L (faint yellow), to Z (light yellow). Completely colorless diamonds are rare.

When diamonds are formed with traces of other minerals, rare and beautiful colors can result. These "fancy" colors range from blue to brilliant yellow to red, brown, pale green, pink, and violet. Because of their rarity, these colored diamonds are highly desirable and may be quite valuable.

Clarity

A diamond's clarity or brilliance is measured by its visible flaws. Those with the fewest blemishes have greater value. Tiny surface blemishes or internal inclusions -- even those seen only under magnification with a jeweler's loupe -- can alter the brilliance of the diamond. Clarity levels begin with Flawless (F & IF) and move down to Very Very Slight (VVS1 & 2), Very Slight (VS1 & 2), Slightly Included (SI1 & 2), and Included (I1, 2 & 3).

Carat Weight

The size of a diamond is measured, not by its dimensions, but by weight. One carat, the traditional unit of measure for diamonds, is equal to approximately 0.2 grams. You may also hear the weight of a diamond referred to in points. A point is equal to 1/100 of a carat; therefore, a 75-point diamonds equals 0.75 carat. Diamonds of equal weight may appear slightly different in size, depending on their depth and proportions. Because they are quite rare, larger diamonds of gem quality are much more valuable.