Carat Weight:

The size of a diamond has the biggest impact on its price.
The metric carat, which equals 0.20 gram, is the standard unit of weight for diamonds and most other gems. If other factors are equal, the more a stone weighs, the more valuable it will be. How "big" is a carat? Many people would like to "understand" carat sizes in real terms. Here's a simple trick to get an idea. Simply take a ruler and look at the table below. These are approximate: Sample carat-weight to diameter-widths for popular sizes.

• 0.25 ct. –3.9mm- 4.1 mm
• 0.50 ct. –5.mm- 5.2 mm
• 0.75 ct. –5.7mm- 5.9 mm
• 1.00 ct. – 6.1mm-6.5 mm

Colour:

The colour of a diamond has the second biggest impact on its price, after carat weight.

Did you know that diamonds come in every colour of the rainbow. Grading colour in the normal range involves deciding how closely a stone's body colour approaches colourlessness. Most diamonds have at least a trace of yellow or brown body colour.

With the exception of some natural fancy colours, such as white, pink, purple, or red the colourless grade is the most valuable. If a diamond does not have enough colour to be called fancy, then it is graded in a scale of colours ranging from Colourless to Light Yellow, "D" through "Z". A diamond with a "D" colour is considered to be colourless. If the colour is more intense than "Z", it is considered fancy.
A fancy yellow diamond fetches a higher price than a light yellow diamond.

Colour

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

FANCY

Scale

Colourless

Near Colourless

Faint Yellow

Very Light Yellow

<-Light Yellow->

COLOUR

Clarity:

The clarity of a diamond refers to how clear, or "clean" the diamond is. The more "clean" the diamond, the higher the price. Most diamonds have "imperfections" in them. They include either black or white natural internal inclusions. The clarity scale is a measure of the severity of those imperfections or "inclusions" as it is known in the trade.

The following is the GIA Diamond clarity-scale:

Clarity	FL	IF	VVS1	VVS2	VS1	VS2	SI1	SI2	I1	I2	I3
Scale	Flawless - Internally Flawless		Very Very Slightly Inclusion		Very Slight Inclusions		Slight Inclusion		Inclusions
Not visible to naked eye Inspection requires 10x magnification									Visible to naked eye

Cut:

The cut of a Diamond is the only property which is totally dependent on man.

Cut refers to not only the shape of the diamonds, but its proportions and finish, factors which determine the sparkle of the diamond. The goal in terms of extracting the greatest beauty from a Diamond is to have light enter a Diamond, disperse the light as it bounces inside the Diamond. Thereby producing the different colours and sparkly effect and finally returning as much light to the eye as possible.