Why blue diamonds?

The diamonds in NDB’s battery have a beautiful blue hue, thanks to the trace amounts of boron contained in their carbon structure. These blue diamonds are artificial, but are reminiscent of true blue diamonds, which are some of the rarest gemstones on Earth. According to findings from an August 2018 study in Nature, they’re formed in Earth’s lower mantle, which is about 660 to 2 700 km below the surface. As such, you can only find blue diamonds in three mines in the entire world, which helps explain their hefty price tag: roughly $15 700 for a 0.3 carat light blue diamond, and $75 000 for a 0.25 carat dark blue diamond.