rare blue diamond which could set a world record price per carat when it is sold in May has gone on show in London. Smaller than a penny piece, it is worth between $5.8m (£3.9m) and $8.5m (£5.7m) according to estimates by its sellers. Discovered in 2008 at the Cullinan mine which also produced the 530 carat Great Star of Africa diamond, which is set in the Crown Jewels.
