Cut - Diamonds, regardless of their shape, get their scintillation and radiance by cutting and polishing the diamond facets to allow the maximum of amount of light that enters through its top to be reflected and dispersed back the same way. A diamond that is cut correctly should catch the light beautifully.
Color - Diamonds come in all colors, ranging from light yellow to white. The most frequently sold diamonds are white. The best color of diamond is having no color at all because, if it is cut well, the light can pass through it effortlessly.
Carat - A diamond's weight is measured in carats. As the weight of the diamond increases so does the price. One carat is equal to 100 points. For example and diamond weighing 25 points is .25 carats. It is important to note that two diamonds can be of equal carat weight, but can differ in their cut, color and clarity. This can also change the price point of the gemstone.
Clarity - A diamond's clarity is determined by the location and number of blemishes in the diamond when viewed under 10 power (10x) magnification. The Gemological Institute of America, a leading authority on gemstones, has a diamond grading scale that ranges from flawless to imperfect 3. Many diamonds contain tiny marks known as inclusions. An inclusion can tamper with light reflecting through the diamond, therefore affecting its value. Always remember: the fewer inclusions, the more valuable the diamond.
The value of emeralds, rubies and sapphires also depends on the four c's: cut, color, clarity and carat.