Clarity

Clarity refers to the purity of a diamond. It judges how free the diamond is from imperfections. Clarity grades range from internally flawless (IF) to fairly included (I3). The higher the clarity grade, the more highly valued the diamond is (and the more rare it is!). Diamonds with no (or very few) inclusions are more highly valued than those with lower clarity both because of their rarity and their visual appearance.

Flaws in diamonds come in many forms, some almost impossible to see and some visible to the naked eye. Typical flaws are:
Pinpoint: A small white dot on the surface of the stone
Carbons: A small black dot on the surface of the stone
Feathers: Small cracks within the stone
Clouds: Hazy areas within the diamond
Crystal Growth: A small crystalline growth that looks like a small diamond within the bigger diamond

The clarity grades used by the Gemological Institute of America are: IF - FL: Flawless or Internally Flawless diamonds show no inclusions of any sort under 10X magnification when observed by an experienced grader. Internally Flawless diamond may have some minor blemishes.
VVS1 - VVS2: Very, Very slightly included diamonds contain minute inclusions that are difficult for experienced graders to see under 10X magnification.
VS1 - VS2: Very slightly included diamonds contain minute inclusions such as small crystals, clouds or feathers when observed under 10X magnification.
SI1 - SI2: Slightly included diamonds contain inclusions (clouds, included crystals, knots, cavities, and feathers) noticeable to an experienced grader under 10X magnification.
I1 - I3: Included. These diamonds contain inclusions obvious under 10X magnification that may affect transparency and brilliance.

Well-cut diamonds with many facets (such as round brilliant) can make it difficult to see inclusions with the naked eye or magnification. Therefore, the best value in these cuts is often SI1 or VS1. Step-cut diamonds (such as Asschers and emerald) are more transparent and show inclusions easier, so a VS2 diamond or higher is recommended.

Many people buying diamonds make clarity the least important of the four Cs. This is because the differences in some grades is very difficult to see except under magnification, and the difference between an SI2 and a VVS1 diamond may not be seen except by a professional gemologist. This allows the purchaser to choose a reasonable clarity diamond and invest more in the color or carat weight of the diamond. Clarity differences have a significant effect on the value of a diamond. The cost of an IF diamond is much higher than a VSI1 clarity, even though the average consumer cannot see the difference!