Could colour diamonds add a sparkle to your portfolio?

The rock now gracing Taylor Swift’s finger, along with US president Donald Trump’s doubling of tariffs on goods from India, has given a welcome boost to the diamond industry. Swift’s engagement lifted the shares in some listed jewellery retailers, while India cuts and polishes most of the world’s diamonds – and Americans are the biggest consumers of diamond jewellery, as Jinjoo Lee notes in The Wall Street Journal. But the lift to diamond prices is unlikely to last much longer than Swift’s wedding cake. That’s because the rise of an almost unlimited supply of synthetic colourless diamonds has tarnished the industry. Colour diamonds, on the other hand, have proved much more resistant.

That’s down to a number of factors, not least of which is the rarity of colour diamonds relative to colourless ones. Only around 0.01% of gem-quality mined diamonds are colour diamonds of the “fancy” type (a measure of the intensity of colour in the Gemological Institute of America [GIA] grading system). They are vanishingly rare. And, naturally, every single one is a little bit different, not only because of the varying sizes, hues, tones and saturations, but also because of the presence of imperfections within the diamonds, known as “inclusions”. So, tracking valuations for colour diamonds is tricky. But with that caveat in mind, prices for fancy colour diamonds have grown at a compound annual rate of 5.7% a year for the past two decades, according to the Fancy Color Research Foundation (FCRF).

How much has the most expensive colour diamond sold for?

This summer, a 10.38-carat pink diamond once owned by Duchess Marie-Thérèse d’Angoulême, the only surviving child of the ill-fated French queen Marie Antoinette, sold for almost $14 million with Christie’s in New York. The record of the most expensive colour diamond ever sold at auction also belongs to a pink gem – the 59.60-carat Pink Star, which fetched $71.2 million with Sotheby’s in Hong Kong in 2017. These prices are not surprising when you consider the lengths to which nature has gone to make them.

Diamonds are created under immense pressure deep underground over millions, if not billions, of years. Yellow diamonds – the most common, although still incredibly rare – contain nitrogen, while blue diamonds contain boron and black diamonds graphite. But pink diamonds get their colour not from impurities, but from the extra stresses they received during their formation that altered their lattice crystal structure. The same goes for red diamonds, which are really just an extension along the colour scale of pink diamonds. They are the rarest of all, and only a handful exist in the world. And since the closure of Rio Tinto’s Argyll mine in Australia in 2020 – which had been responsible for 90% of the world’s supply of newly mined pink diamonds – no more or very few are now coming onto the market. Small wonder, then, that, last month, police in Dubai arrested a gang of thieves who had gone to great lengths to steal a 21.5-carat pink diamond. It had been valued at $25 million.