The unit of weight used for diamonds is the carat. For smaller stones carats are further divided into 100 points.
Clarity is determined by examining a stone for the placement and number of irregularities. The fewer the inclusions the more valuable the stone.
The most desirable color for a diamond is true white or colorless. Diamonds are given a letter from D to Z to determine how far from colorless they appear.
The cut determines sparkle in a diamond. When light enters a well cut stone, it reflects off of the facets and returns to your eye as brilliance and scintillation.