GIA has created the universal standard of assessing the quality of any diamond anywhere in the world, this is known as the 4Cs of Diamond Quality- COLOR, CLARITY, CUT & CARAT WEIGHT.
The color of a diamond is one of the derminants of its value. White diamonds are priced according to how colorless they are, the least the amount of yellow-tint the more valuable it is. However, it is not always the case that colorless diamonds are more expensive than colored ones. Fancy yellow, blue and pink diamonds are considered more rare than white diamonds that is why they are priced much higher.
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Clarity is gauges the purity of the diamond, this is guaged by how much blemish and inclusions there are in a stone. By blemish we mean external and by inclusions we mean internal impurities.
There are 6 main categories of diamond clarity:
Cut is used to describe the precise shape and positioning of a diamond’s facets -- This is what makes a diamond sparkle, the topmost criteria to a stone’s beauty. The sparkle varies on the cut grade of a stone and determines how the light interacts with the diamond. Factors that affect the cut are; Brightness (Internal and external white light reflected from a diamond), Fire (The scattering of white light into all the colors of the rainbow) and Scintillation (The amount of sparkle a diamond produces, and the pattern of light and dark areas caused by reflections within the diamond).
The Cut-Scale is as follows:
Carat is specifically a measure of a diamond's weight, and by itself may not accurately reflect a diamond's size. Below is a chart to show comparison of the progression of the carat weight.
*This chart is not actual size.