Emerald is beryl coloured green by chromium or vanadium, the same mineral as aquamarine with a different trace element. It is 7.5 to 8 on the Mohs scale, hard, but almost every emerald contains inclusions and internal fractures, which jewellers call the jardin, the garden. That is why cut emeralds are usually oiled to fill surface-reaching cracks, and why they are more fragile than their hardness suggests. Most comes from Colombia, Zambia and Brazil. Hand-picked in St Andrews and posted UK-wide.