Chief executive Jeff Bezos, 40, announced that the group is to launch into selling jewellery in the US, having tested the new site on more than 100,000 customers. He said: 'While the average margin in jewellery retailing is approximately 45% to 50%, we target substantially lower margins and even lower - about 13% - on diamond jewellery. This is in keeping with our strategy of driving growth through lower prices.'