May’s birthstone is Emerald, that fabulous beryl gemstone, named from the Greek for ‘green’.  It is  one of the original ‘precious gemstones’, famed for its rich green colour, first mined in Egypt from 330BC, but nowadays there are two main sources – Columbia and Zambia. The availability of fine quality emeralds is limited and treatments such as glass filling are widespread, in order to produce enough commercially viable stones. Legend has it that emeralds have the power to make the wearer more intelligent and quick-witted.  It was once also believed to cure diseases such as malaria and cholera.  Its...