The 4 Cs:

• Carat Weight
  The size of a diamond is measured in carat weight. A carat is equivalent to 0.2 gram.
  
  
  
  
  
• Clarity
  Paradoxically, the term clarity is mainly used to refer to the flaws in a diamond.
  The Internally Flawless Grade (IF) describes diamonds which have no internal characteristics, but which have minor surface blemishes that do not penetrate the stone.
  • The VVS1 & VVS2 grades (Very, Very Slight Included) are used to describe diamonds which have very, very small inclusions.
  • The VS1 & VS2 grades (Very Slight Included) are used to describe stones with very small inclusions.
  • The SI1, SI2 & SI3 grades (Slight Included) are used to describe stones with small inclusions.
  • The I1, I2 & I3 grades (Included) are used to describe stones with medium or large inclusions.
• Cut
  The term cut is used in several ways. It refers to the facet arrangement on the surface of the diamond. Brilliance pervades a well-cut diamond. Cut is also synonym for shape. E.g. round, brilliant cut diamond
• Colour
  Diamonds are found in a range of colours, the rarest being colourless or fancy colours such as greens, blues and reds. A letter is assigned to a colour grade. The colour grading scale begins with D, the best colourless stone, to Z. Good stones range from D through I.
  On the opposite end of the spectrum, yellow and pink diamonds have their own grades. Adjectives are used to describe the degree of colour, otherwise known as saturation.