In 1821 two men, Elijah Hamlin and Ezekiel Holmes changed Maine’s gem industry forever, by finding a beautiful piece of green tourmaline on Mount Mica in Paris, Maine. They had no idea the extent of the discovery that they had just made, even after sending it to a Yale professor who determined it was tourmaline. The gem industry was not very popular; up until the 1860’s when serious mining operations began, leading Maine to become world famous for its tourmaline. Now it is the official Maine state gemstone!
Tourmaline comes in a range of colors, some are multicolor like watermelon tourmaline and it is dichromatic changing color at different angles. The color difference is due to different elements being present when the tourmaline is forming.

In the case of watermelon tourmaline the elements present during the formation of the gem change part way through it's formation. We see it as the center being pink and the outer edge being green.