One of the oldest stones in the world are the emeralds of Zimbabwe. Interestingly, one of the world's greatest emeralds is the Mogul emerald weighing 217.8 carats and measuring roughly 10cm.

Stone is of emerald green to dark green colored. Emerald has been hailed as one of the precious gems since time immemorial. The name is from the Greek word smaragdos, the green stone.
More information can be found in an article focused directly on emerald.