The most valuable type of diamond is the red diamond, which is also the rarest of all colored diamonds. Red diamonds, also known as Fancy Reds, come in various shades ranging from orange-red to brownish-red. The majority of the world’s red diamonds come from the Argyle Diamond Mine in Australia[1].
Due to their rarity, red diamonds are the most expensive per carat among all fancy colored diamonds, with an average selling price of over one million dollars per carat[2]. Some of the most famous red diamonds include the Moussaieff Red, which was purchased in 2001 for nearly USD 46 million[3], and the Hancock Red Diamond, a 0.95-carat Fancy Purplish Red round brilliant diamond[3].
In terms of formations, Type IIa diamonds are the rarest, followed by Type Ib. Type IIa diamonds are considered the most chemically pure and are very expensive. Some of the world’s most famous and opulent diamonds, such as the Elizabeth Taylor Diamond, The Graff Pink, and the Koh-i-noor (which still sits on the British crown), have been cut from this type of rough diamond[1]. Type Ib diamonds are also rare, making up less than 0.1% of natural diamonds. These diamonds are usually intensely colored, including yellow, brown, and orange diamonds[1].
Other rare and valuable colored diamonds include blue, pink, and green diamonds. Blue diamonds, for example, are more common than red diamonds but still command high prices. A medium-toned 1-carat blue diamond can cost around $200,000 on average[2]. The most expensive blue diamond ever sold was a 14.2-carat fancy vivid blue diamond, which sold for 57.5 million[4]. Pink diamonds, particularly Argyle diamonds, are also among the rarest colored diamonds[4]. Green diamonds are rarer than blue or pink diamonds but are not as valuable as red diamonds[5].
Citations:
[1] https://64facets.com/blogs/blog-all-about-diamonds/worlds-rarest-diamonds
[2] https://www.1215diamonds.com/blog/rarest-diamond-color/
[3] https://www.leibish.com/what-are-the-rarest-colored-diamonds-article-543
[4] https://www.gemsociety.org/article/most-expensive-diamond-colors-with-prices/
[5] https://www.astteria.com/blog/which-of-the-colored-diamonds-is-most-expensive/
