The four c's refer to the cut, clarity, colour, and carat or weight of diamonds. Each of the four are very important.
The cut refers to those parts of the diamond which determine its reflective properties.
Diamonds that are poorly cut do not return the light that enters, leaving both their beauty and their value diminished. If the cut is poor, the quality of the other three Cs cannot save a diamond's value.
The coloring of a diamond is another of the factors that determine its price. Other than white, or colorless, there are several different colors of diamonds. These can include orange, blue, yellow, green, red, brown, and the very rare pink and light blue. White (colorless) diamonds are the most popular.
Clarity of a diamond is a quality that can produce a marvelous stone. Poor clarity may produce a dull, dead, or even a lifeless stone. Clarity can be referred to by other terms, such as purity or quality. The term clarity means clearness.
The clearness of a diamond allows the passage of light without obstruction. Stones with exceptional clarity exhibit no inclusions and/or carbon spots that interfere with the passage of light.
Due to their rarity, diamonds of unusual color can be more expensive than similar stones without color.
Carat refers to the weight of a diamond. This plays a major role in value and price. Large diamonds are rare compared to small diamonds. The limited supply of larger diamonds creates a high demand making them very expensive.