Lab-grown diamonds are having a moment. Thanks, as always, to social media and the increasingly jaw-dropping engagement rings displayed by celebrities like Ariana Grande, Hailey Bieber and – of course – the Kardashians, millennial and gen Z women want to buy bigger, blingier jewellery.  Sadly for us civilians, a six-carat mined diamond like Bieber’s oval cut solitaire might cost $500,000. Its lab-grown counterpart, however, comes in at a third of that.