What Makes Pink Diamonds Pink

Washington, 24 December 2014 - They're one of the world's rarest jewels - but nobody knows for certain why pink diamonds are pink.

That hasn't stopped investors from snapping them up at auction and sending prices skyrocketing. In October a new world record was set at a Sotheby's sale in Hong Kong when an 8.41-carat pink diamond sold for $17,768,041 (£11,438,714) - more than $2.1m (£1.8m) a carat.

"Everybody's talking about them, and everybody loves them," says Jeffrey Post, curator of the National Gem and Mineral Collection at the Smithsonian's National Museum of Natural History in Washington, DC. "Yet you can't tell people why they're pink."

Other diamonds get their colour from chemical impurities that absorb light. Yellow diamonds contain traces of nitrogen, and blue diamonds contain boron. But no similar impurities have been found in pink diamonds, leading scientists to speculate that the colour may be the result of some kind of seismic shock that altered the stone's molecular structure.

It's now hoped that a cache of brown and pink diamonds from the Argyle mine in Western Australia may solve the mystery.