Origin and Diamond Market
Diamond has a bloody history right from Cleopatra to the famed Koh-I-Noor which at the earliest recorded date, 1526 AD, weighed 793 carats before being reduced to 186 carats by the lapidary Borgio.

Today De Beers monopolizes diamond production and trade which is around 130 million carats annually and in addition. A diamond is weighed in units of carats and a carat originally meant the weight of one carob seed. The present standard carat is, however, metric and equals 0.2 gm or 1/42 of an ounce.

How to Buy Diamonds
Diamonds mined out (mainly in South Africa and Botswana) can't be sold directly as these are raw.

The 4Cs which stand for carat, clarity, color and cut of diamonds, determine the quality and price of these gems.

Carat: A carat equals 0.2 gm in weight and further divided into 100 points. This means a quarter carat equals 25 points and is written as 0.25 ct. It is hard that one can avail a diamond weighing a carat or above these days. It is almost always in fractions of carats now.

Clarity: Clearer the diamonds higher are the costs. Tiny inclusions (impurities due to presence of other minerals) mask the brilliance. While costing, the numbers of inclusions, their colors, positions are considered. Fewer the inclusions, greater is the reflection and higher is the value. Clarity is graded from I3 to VVS1, starting from Very Noticeable Inclusions to Very, Very Slightly Included, in decreasing order.

Color: The best color for diamond is having no color. White light passed through it will come out in rainbow colors. Although most diamonds look colorless they are slightly yellow or brown with subtle shades. Proximity to being colorless raises the value.

Cut: Cut is the dictator of a diamond's value. A best cut diamond reflects all the light without allowing it to pass through giving it the brightest of shines. The best cut diamond has 57 facets (cut and polished faces) with 33 of them being on the top half, crown, and the rest on the pavilion, bottom half.

Mathematically this gives the total reflection. The best cut diamond will have a round shape with the pavilion having an included angle 600 albeit there is a complex guidance chart for cutting diamonds.