The value of a diamond is based on the four c's: carat, cut, clarity, and color.
Carat is the weight of a diamond. One carat equals 1/5 gram.
The cut of a diamond is it's shape after a jeweler finishes it. The four most common cuts are pear, emerald, marquise, and brilliant.
The clarity of a diamond is how pure it is. Diamonds can range from flawless to heavily flawed.
The most common colors of diamonds are white, yellow, and brown. Diamonds can also be blue, red, orange, purple, green, and even black. A very brightly colored diamond is called a fancy. Fancies are rare and worth a lot of money.