Meidan-i-Noor

The Meidan-i-Noor emerald reputedly measues 5 cm in height and was discovered in 1957 in Colombia by a local mining family.
Its name means "Field of Light" in Persian.
The gem was brought to Europe by an un-named millionaire and kept in a private collection in Vienna until the mid 1980s. Sold for an undisclosed amount to a Manhattan jeweller, the emerald was en route to New York when it was stolen from a Japan Ocean Trust bank safe in London during a bizarre heist where six people (four men and two women who worked at the bank) were caught and charged, but seemed to be operating separately.
Three of the men were professional jewel thieves working for a gang known as The Cowboys.

The emerald was never recovered, and to this day its location remains a mystery.