One of the largest rough pink diamonds ever discovered was recovered by miners in Angola in 2022. Called the Lulo Rose, it weighs an impressive 170 carats and could become the most expensive diamond in history. Its enormous weight is one factor, but so is its rare pink colour, which made us wonder: why are some diamonds pink?
Coloured diamonds are rare, accounting for about 0.01 per cent – one in 10,000 – of diamonds mined around the world. Pink is just as rare as blue, green, purple, orange and red, while yellow and brown are slightly more common.
Curiously, while the rarity of coloured diamonds drives up their price, the aesthetic hues are the result of imperfection – something we humans tend to devalue. The reason we dig up more clear diamonds is that in a one-component rock like diamonds, it’s more common to end up with a chemically pure one.
The exact mechanism behind pink diamonds isn’t known for sure, but it’s thought to be the result of distortion, which is one of the three main ways a diamond can end up with imperfections (the other two being impurities and damage). Distortion occurs when a diamond’s lattice structure is twisted and bent, changing the way light is reflected so that it doesn’t appear white.
This distortion has to be just right to be pink, as a little more and it becomes brown. The colour of a diamond is always the result of the exact conditions in which it was forged, which is why diamonds with imperfections never look the same. Not all pink diamonds are the same shade of pink, and not all green diamonds are the same shade of green.
However, it makes sense that around 80 to 90 per cent of all pink diamonds found by man have been discovered in the same mine, because they were forged in an area that has the same geological history. That mine was the Argyle in Western Australia, which is now closed but was the site of a continental collision around 1.8 billion years ago.
The collision provided plenty of pressure, while their position near the base of the lithosphere provided plenty of heat, which combined to create just enough distortion to produce a range of diamonds from pale pink to red, brown, orange and purple. Among them were many pink diamonds, but none as large as the Lulo Rose.
Before its discovery, the largest and most expensive pink stone was the Pink Star, which sold for a spine-chilling $71.2 million at a Hong Kong auction in 2017, making it the most expensive diamond ever sold. It originally weighed 132.5 carats, but was cut down to 59.6 carats, leaving many to wonder if the 170-carat Lulo Rose could one day take the crown as the most expensive diamond in history when it comes up for auction.
Get your wallets ready, folks.
