diamond (as gemstones)

See also diamond as an abrasive.

The largest diamond thus far discovered is the Cullinan, found in 1906 at the Premier Mine in South Africa. It weighed 3,106 carats, about 1¹/3 pounds, and was roughly 2 inches by 2½ inches by 4 inches. Cut, it made nine important gems and 96 smaller brilliants, with 9½ carats of leftovers. The largest of the gems, weighing 530.2 carats, was named the Great Star of Africa and mounted in the British Royal Sceptre. The next biggest, 317.4 carats, became part of the Imperial State Crown.

The largest diamond ever found in the United States is the Uncle Sam Diamond, 40.23 carats, found in 1924 at the “Crater of Diamonds” near Murfreesboro, Arkansas. It was cut to make a 12.42 carat emerald-cut gem.

Clarity

In descending order of desirability: 

Grade Symbol Description Under this type of examination
Flawless F No inclusions or blemishes.
Internally Flawless IF No inclusions are visible. 10x magnification
Very Very Slightly Included #1 VVS1 Inclusions are extremely difficult to locate.
Very Very Slightly Included #2 VVS2 Inclusions are very difficult to locate.
Very Slightly Included #1 VS1 Minor inclusions that are difficult to locate.
Very Slightly Included #2 VS2 Minor inclusions that are somewhat difficult to locate.
Slightly Included #1 SI1 Noticeable, easy to locate inclusions.
Slightly Included #2 SI2 Noticeable, very easy to locate inclusions.
Slightly Included #3 SI3 Visible inclusions. naked eye
Included #1 I1 Inclusions somewhat easy to locate.
Included #2 I2 Inclusions easy to locate.
Included #3 I3 Inclusions very easy to locate.

Color

Perfectly colorless diamonds are very rare.

  Commercial Grade
D, E, F Collection White
G, H, I White
J, K, L Commercial White
M, N Top Light silver
(Top Light Cape)
O, P, Q, R, S Light Silver
(Light Cape)
T, U, V, W Silver
(Cape)

Caret Weight

Cut

In addition to weight, cut diamonds are sized by the size of the table, the flat surface on the top of a cut diamond. On a round brilliant, table size is measured from opposite corners. On fancy shapes, it is measured from corner to corner across the narrowest diameter; on step cuts, from side to side across the narrowest dimension.

The cut which produces the most fire in a diamond is the Tolkowsky theoretical brilliant cut, worked out by Marcal Tolkowsky. Its proportions are shown in the drawing below. Today a slightly larger table than is optimal is usual; instead of 53% of the diamond's diameter, 57% or even 60%.

Drawing of Tolkowsky cut

Resources

www.77diamond.com

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