Here, briefly, is how each of the Four Cs contributes to a diamond's value:

§ Carats: Diamonds can be measured by weight, and the scale used is "carats." The larger a diamond is, the heavier it is - that's obvious - so a one-carat diamond is larger and heavier than a half-carat stone. Large diamonds are also rarer, and the rarer a diamond is, the more valuable it is.

§ Clarity: The clearer a diamond is - that is, the less marred by internal inclusions - the more pleasing it will be.

§ Colour: Some diamonds have colour or hue. Traditionally, the ones with the least colour (referred to as white) are considered the most beautiful - consequently they are also the most valuable.

§ Cut: The more precisely a diamond is cut, the more it will capture and reflect light, and the more brilliant it will appear.