(IDEX Online) - Gen Z and millennials don't realize their "sustainable" lab growns are made by burning coal in China and India, according to a Fortune investigation.The global business magazine says many manufacturers are based in India, where 75 per cent of electricity comes from burning coal, but still use words like "sustainable" and "environmentally-friendly" to promote goods on their websites.It says Cupid Diamonds claims to produce its stones "an environmentally friendly manner," but did not respond to a request for details.More than half of China's electricity came from coal in 2023. Fortune asked some of the country's largest producers - Henan Huanghe Whirlwind, Zhuhai Zhong Na Diamond, HeNan LiLiang Diamond, Starsgem Co. and Ningbo Crysdiam - about their electricity sources. None of them responded.Pic of rough lab growns, courtesy Huanghe Whirlwind.