What is the price per carat on rare blue diamonds?

Diamonds that are naturally blue are among the rarest of diamonds.

Recently the 5.16 carat Sky Blue Diamond sold in Hong Kong for US$6,400,000, or $1,240,310 per carat. This stone known as the De Beers Millennium Jewel 11, represents the creme de la creme of blue diamonds.

According to its GIA certificate, it is a "... natural, Fancy Vivid Blue colour, Internally Flawless clarity."

Read more about this stone, below.

Because of its rarity and desirability, treating a naturally clear diamond to make it look blue -- which will only occur if the diamond already contains boron -- is one way a jeweler can increase the profit made on the sale of a diamond.

Treated diamonds should be documented as treated stones. Gemologists will always be able to detect modification of a diamond, which devalues the gem.