The 4 'C' of Diamond is - Cut, Clarity, Color and Carat

Cut

The cut of a diamond determines how it reflects light, which is responsible for its sparkle or brilliance. A well-cut diamond is cut by a skilled professional to the best proportions possible so that light will be reflected from each of its mirrorlike facets and disperse through its top. Too shallow a cut will let light escape through a diamond's bottom, causing it to appear dull, while too deep a cut will allow light to be lost through a diamond's sides, making it appear dark.

Because a diamond with perfect color and clarity could nevertheless have poor brilliance if it is not well cut, many gemologists consider this to be the most important property to note when choosing a diamond. Diamonds can carry cut grades of Excellent, Ideal, Very Good, Good, or Fair.

Clarity

No two diamonds are alike. A diamond's most distinguishing characteristics are its inclusions, marks that are often invisible to the naked eye. However, under a jeweler's magnifying loupe or microscope they can look like crystals, tiny rivers, or clouds. A diamond's clarity is determined by the presence or absence of inclusions--fewer inclusions mean better clarity--and how visible they are. The greater a diamond's clarity, the greater its brilliance and value. A diamond categorized as internally flawless will have no inclusions, but this is extremely rare.

Diamonds with very, very small inclusions are graded as VVS1 or VVS2. Those with larger inclusions are considered lower-grade. Diamonds with inclusions that are visible with the naked eye are graded I1 to I2.

Color

Though diamonds come in a wide range of colors, colorless diamonds have traditionally been considered the most valuable. Most diamonds are graded on a scale using the letters of the alphabet, from D (colorless), the best grade, through Z (a light yellow). It is difficult for the untrained eye to notice such variations in color unless stones are being compared side by side. The comparatively rare colored diamonds are known as fancy-colored and are also quite valuable. They range in hue from the more common yellow (also graded Z+ on the alphabetic scale) to pink, blue, green, red, and even black and white.

Diamonds that are graded D, E, and F tend to be the most expensive because of their rarity. However, any diamond you buy should have a good balance of cut, color, and clarity, so as to impart the most brilliance and dazzle possible

Carat

A diamond's weight is measured in carats, with one carat being equivalent to 100 points. You will often see a diamond referred to as a 3/4-carat stone or a 75-point diamond. Larger stones are often more highly valued, but size should not be the only consideration--high brilliance, which varies according to clarity, cut, and color grade, is highly desirable in a diamond.