Diamonds were once a girl’s best friend, according to Marilyn Monroe in the 1953 classic film Gentlemen Prefer Blondes.

But these days, for environmentally conscious customers, lab-grown gems seem to be preferred over mined rock, with celebrities such as Taylor Swift, Reese Witherspoon and Emma Watson showing off lab-created accessories.

The boom of lab-grown rocks has upset traditional mining firms such as Anglo American, the owner of De Beers, the world’s leading diamond company, according to The Times.

The FTSE 100 company’s shares dropped by 20 per cent after it announced production cuts at its mines. Meanwhile, De Beers sold just $80million of rough diamonds at the end of October, compared with $454million a year earlier, BNN Bloomberg reported.

In comparison, the lab-created variety – regarded as more ethical and sustainable than those from mines – appears to be on the up; 10 per cent of diamonds sold in 2022 were lab-grown compared to only 2 per cent in 2018.

De Beers had been saying ‘a diamond is forever’ since 1948, when ad exec Mary Frances Gerety dreamed up the slogan.

But 75 years on and diamonds are having an identity crisis. ‘Rough diamonds of a size that would usually be employed for engagement rings have gone down in price,’ explains London-based​ jewellery journalist and consultant Milena Lazazzera. ‘The industry is under pressure.’

Announcing unremarkable sales figures in June, the CEO of De Beers Group referred to ‘global macroeconomic challenges’ and described the industry’s mood as ‘cautious’.

Natural diamonds are made of pure carbon below the earth’s surface. Lab-grown diamonds are the result of an industrial process as opposed to a geological process, but they are made of the same composition.

You can generally get a 50 per cent larger diamond for your budget when choosing laboratory grown, according to Gary Ingram, CEO of TheDiamondStore.co.uk, the UK’s largest diamond retailer.

Many famous faces have already jumped on the lab-grown diamond bandwagon, with Meghan Markle sporting a pair of earrings featuring sustainable gems created by London-based brand Kimai while visiting Smart Works in the city in January 2019.

Leonardo DiCaprio is also a fan, and has invested in Diamond Foundry, a San Francisco-based lab-grown jewellery start-up.

‘With lab-grown diamonds, you can get something that is exceptionally high quality for a dramatically lower price point,’ Lindsay Reinsmith, co-founder of the California-based company Ada Diamonds, told The Times.

‘They do require energy to be grown, but that energy is a fraction of what’s needed to mine them.’

Two techniques are used to create lab-grown diamonds. HPHT (High Pressure High Temperature), invented in the 1950s, mimics the high pressure and temperature found in the earth when natural diamonds are formed.

A ‘seed’ (chip of diamond) is placed into a piece of carbon, and the pressure and temperature used forces the carbon to form a diamond.

CVD (Chemical Vapour Deposition) is more expensive, often producing higher grade diamonds.

A thin slice of diamond is placed in a vacuum chamber filled with carbon-heavy gases. Under 1,000c, the gases turn into plasma which bonds with the diamond slice to build the diamond in layers.

Diamonds can be grown in any size or colour, but the big appeal for environmentalists is that they’re supposed to be gentler on the Earth – and on humankind.

The lab-grown variety doesn’t pollute water sources or destroy habitats. They’re not mined in war zones or sold to finance bloody conflicts. Evidence of ‘blood diamonds’ emerged from Sierra Leone’s civil war in the 1990s, inspiring the Leonardo DiCaprio film Blood Diamond.

But lab-grown diamonds aren’t without fault. ‘There is a massive energy expenditure when a diamond is created and it’s important it’s not sold as a green solution,’ Helen Dimmick, a gemologist and jewellery expert, told The Daily Mail in 2021.

‘Not all lab growers are created equal,’ agrees Joanna Park-Tonks, founder of British jeweller Chelsea Rocks, who is calling for more regulation. ‘We need to build trust and establish standards.’

Others say the mining industry is being unfairly tarnished with past wrong-doings.

In May 2023, it was revealed that more than a third of engaged men proposed with a lab-grown diamond ring last year as sales of man-made stones plummeted.

Research by wedding website The Knot found the number of couples opting for lab-grown stones had more than doubled since 2020 after major jewellery brands such as Pandora started offering the sustainable alternatives.

At the same time the amount of engagement rings with natural diamonds fell by around 25 percent, according to an independent diamond industry analyst Edahn Golan.

Experts said the trend is being driven by couples wanting super-sized stones – made more accessible by the cheaper cost of the lab process.

The survey found that 36 percent of engaged couples opted for a lab-grown ring, up from 18 per cent in 2020.