On a grey January morning in 2019 Meghan Markle emerged onto a London street on her way to a meeting. She wore a smart coat and heels, but it was not her clothing that caught the attention of the world. It was a pair of glittering drop earrings embedded with diamonds that had been grown in a lab.

It took just five days to grow the diamonds adorning Markle’s ears according to Sidney Neuhaus, co-founder of Kimaï, the company that made them. Based in Antwerp, the capital of the world’s diamond business, both she and her co-founder Jessica Warch grew up in diamond families. Nauhaus’s father owns a diamond jewellery shop, and her grandfather worked for De Beers, making his career in diamonds after World War Two.

Despite their illustrious family histories in the trade, Neuhaus and Warch chose to break away from conventional diamonds because of the environmental and humanitarian toll of extracting them. Millennials and now Generation Z – who together are the main purchasers of diamonds for engagement rings – are moving away from conventional diamonds, with nearly 70% of millennials considering buying a lab grown alternative. (Read more about the rise of guilt free gems.)

So what are lab grown diamonds, and are they really a more sustainable alternative to traditional mined diamonds?

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First up, a lab-grown diamond is a diamond: chemically, physically and optically identical to a mined diamond. Naturally occurring diamonds are forged in the crushing pressure and immense heat of the Earth’s mantle around 100 miles underground. Most were formed between 1bn and 3bn years ago at a time when our planet was hotter than it is today.