Blue diamonds —or type IIb diamonds —are the rarest diamonds on Earth. These diamonds contain boron which leads to blue color in diamonds. Less than 0.1% of all natural diamonds are Type IIb diamonds. World’s famous 45.52 ct “Hope Diamonds” is the best example of Type IIb diamond.
A recent survey showed that blue diamonds have a surprising “Superdeep” origin and a link to ancient oceans, says GIA study published in Nature. Boron from ancient ocean floor creates color in rare ‘superdeep’ diamonds. These gemstones form four times as deep in the Earth as their colorless cousins, the new report indicates, at depths of at least 400 miles below the surface.
Reference:
https://www.washingtonpost.com/news/speaking-of-science/wp/2018/08/01/geologists-discover-the-extreme-origin-of-blue-diamonds-earths-rarest-kind/
https://www.livescience.com/63233-blue-diamonds-deep-boron.html
https://www.gia.edu/blue-diamonds-have-surprise-origin-and-link-to-ocean