Diamonds more than any other gemstone have the capability to produce the maximum amount of brilliance. Whilst almost all diamonds contain minute traces of non-crystallised carbon or small non-diamond crystals, one that is virtually free of interior or exterior inclusions (commonly clawed flaws) will be of the highest quality. In such a diamond nothing interferes with the passage of light through it; thus it's clarity only serves to intensify it's beauty and fire.
To determine a diamonds clarity it is viewed under a 10x magnification by a trained eye. What minute inclusions there are make every diamond quite unique. They are natures fingerprints and neither mar it's beauty nor endanger it's durability. However, the fewer seen, the rarer the stone will be.