Gems: Fancy diamonds.
At the words "high quality diamonds" in our mind, most likely, arises a picture of sparkling colorless stones. But there are exceptions – 
fancy colo red diamonds with bright, saturated color. While fancy diamonds can be of different colors (blue, green, purple, yellow and orange), natural red diamonds are the rarest gems, with the highest market price per carat. In fact, a very small number of diamonds have been certified as red diamonds.
Natural colo red diamonds
Some colo red diamonds gain their color from impurities of other elements, for example: boron colors stone in blue, and nitrogen - in yellow. But there are diamonds which owe their color to defects in the crystal structure of the stone. Since red color appears because of a mechanical defect or pressure in a diamond during 
its movement to the surface. It is conside red that these defects block the electrons in such a way that their interaction with light creates a pink and red color of the diamond.
Artificial red diamonds
The rarity of natural red diamond pushed to intervention of science to balance the supply and demand. As a result, there were artificial red diamonds. Until recently, all attempts to create colo red diamonds ended in failure, as it was impossible to imitate pure red color, which have red by nature diamonds. But the company «Lucent Diamonds» developed a technique that allows to change the color of the usual diamonds. Such artificial red stones are much cheaper than natural red diamonds.
How are they rare?
Argyle diamond mine in Australia - one of the leading manufacturers of fancy diamonds in the world. Argyle annually gives hund reds of millions of stones, but only a small percentage of them are sold as red and pink diamonds. The mine said that only one- carat of pink diamond falls on every million carats of rough diamonds (0.0001%). And because the red diamonds are even more rare then pink, the share of red diamonds should be even lower than 0.0001%.
The relative cost
In 1980, at auction was paid a record price for a diamond: 127 thousand dollars for pink diamond of 7.27 carats. But in 1987, this record was broken by sale of "Hancock Red" diamond with weight of 0.95 carats. This red diamond was bought for 880,000 dollars, more than 926,000 dollars
per carat. In November 2007, a new record was achieved when the ring with violet- red diamond of 2.26 carats was sold at a price of $ 1.5 million per carat.
"Big Three"
Although the largest colorless diamond "Cullinan" weighs more than 530 carats, and of red diamonds only three weigh more than 5 carats. The largest red diamond is " Red Moussali" with weigh of 5.11 carats. Faceted in triangular diamond shape 
("Trilliant" cutting), it was originally called " Red Shield". Name was changed when it was bought for $ 8 million by the jewelry company "Moussalli". "Kazanian Red" - diamond 
with emerald cutting with weigh of 5.05 carat and "De Young Red" - diamond of round cutting with weigh of 5.03 carats now belong the Smithsonian National 
Museum of the History of America. These three stones are the only "major" red diamonds.
