The world's largest cut emerald is set to go up for auction - and is expected to fetch $1.15million. The 57,500-carat stone, which is the size of a watermelon. The gem, named Teodora, was found in Brazil and cut in India, before being sold to rare gems dealer Reagan Reaney in Calgary - but there are doubts over whether it is in fact a true emerald.
Emeralds - the birthstone for the month of May - get their green colouring from the presence of chromium within the stone and the effect it has on constituent mineral beryl. Unlike diamonds they are graded by eye. If when examined by the naked eye an emerald appears free from material trapped while it was being formed then it can be considered flawless.
Emerald crystals, like all other naturally occurring gemstone crystals, grow one molecule at a time meaning it takes prolonged periods to create a quality gemstone.