Carat Weight

The larger the carat weight, the more expensive the diamond is, both in total price and on a per-carat basis. Larger diamonds are found less frequently than smaller diamonds. As a result of their relative rarity and the economic forces of supply and demand, one 2-carat diamond will be more expensive than two 1-carat diamonds of the same quality.One carat equals 200 milligrams in weight. For diamonds under one carat, each carat is divided into 100 points - similar to pennies in a dollar. 0.75 ct. = 75 points, 1/2 ct. = 50 points..

Clarity Grade

The less inclusions in a diamond, the higher its quality. Clarity is determined on the location, size, number and type of inclusions. Because natural diamonds formed under conditions of tremendous heat and pressure, it is extremely rare to find a diamond lacking any internal and external characteristics. These characteristics are a byproduct of its formation.

The GIA Clarity Scale includes eleven clarity grades ranging from Flawless to I3. F/IF (Flawless / Internally Flawless) diamonds show no inclusions under 10X magnification, these are very rare and expensive diamonds. VVS1/VVS2 diamonds are very, very slightly included with minute blemishes that are extremely difficult to locate under 10X magnification. VS1/VS2 diamonds are very slightly included with minor blemishes that are somewhat easy to see under 10X magnification. At times, the inclusion can be seen without magnification. SI1/SI2 are slightly included diamonds with blemishes that are easily visible under 10X magnification and may be visible with the naked eye. I1/I2/I3 diamonds are included with significant and easily visible blemishes..

Colour

The less color in a diamond, the higher its quality. The common color scale ranges from D (colorless) to Z (light yellow or brown). Although many people think of gem quality diamonds as colorless, true colorless diamonds are actually very rare. Most diamonds used in jewelry are nearly colorless with tints of yellow or brown.D-Fgrades are considered "Colorless" and these diamonds tend to be significantly more expensive.G-Jgrades are considered "Near Colorless" and because the color in these diamonds will be almost undetectable to the untrained eye, this range can offer great value for money.

Fluorescence: Some diamonds emit visible light when exposed to ultraviolet radiation, but fluorescence is not a factor in determining color or clarity grades. However, a description of its strength and color is provided on most lab reports as an additional identifying characteristic of the diamond.

Cut

The better the cut, the more brilliant a diamond is. The common Cut scale is from Excellent to Poor. Most gemologists consider the cut grade the most important attribute of a diamond. A polished diamond's beauty lies in its complex relationship with light: how light strikes the surface, how much enters the diamond, and how and in what form light returns to your eye. The result is a magnificent display of three attributes:
* Brightness is the combination of all white light reflecting from the surface and interior of a diamond.
* Fire describes the "flares" of color emitted from a diamond.
* Scintillation describes the flashes of light you see when the diamond, the light, or the observer moves.

A polished diamond's proportions affect its light performance, which in turn affects its beauty and overall appeal. Diamonds with fine proportions, symmetry, and polish optimize their interaction with light, and have increased brightness, fire, and scintillation.

Image source: Indian Institute of Jewellery