The following is a simple explanation of the 4 C's. For detailed information go to www.GIA.edu
A diamond's value is based on the characteristics known as the "4 C's". Clarity, Color, Cut (proportions not shape) and Carat Weight.
A diamond's clarity is determined by the number, nature, position, size and color of natural internal characteristics called "inclusions". Various characteristics make up these inclusions which can be; crystals, feathers, clouds, black carbon etc. Clarity is measured on a scale ranging from flawless to heavily included. The clarity of a diamond is graded by using a "jeweler’s loupe" with 10X magnification. The final clarity grade is determined by how difficult or easy the inclusions are to see.
Ideally, a diamond should have no color at all. Color is measured on a scale ranging from colorless "D" to light yellow "Z". D, E and F are in the colorless category and are rare. As a diamond gains in color it moves down the color scale.
Cut ensures that a diamond has maximum brilliance and sparkle. Each shape of diamond has proportions that, if met, will bring brilliance or "fire" to the stone. When looking at a diamond, if it doesn't catch your eye or if it doesn't flash in the light, it's probably not cut well. Good cutting, along with good clarity & color, is what brings fire to each diamond.
Carat is the unit of weight for diamonds. One carat has 100 "points" just like a dollar has 100 pennies. A diamond weighing 50 points is 1/2 carat, or 0.50ct. A diamond weighing 75 points is 3/4 carat or .75ct and so on.