Tourmalines are mixed crystals of aluminum boron silicate that also contain elements such as iron, manganese, sodium, lithium, or potassium. Today, they can be distinguished by their chemical composition, and by the optical and physical properties observable by gemological testing.
The gem got its name from the Sinhalese word "Toro Mali" meaning mixed stones of many different colors. Back then, gems were usually just identified by their hues, and so many people weren't really aware that many species of tourmaline actually belonged to the same gem group. The species called "Elbaite", although not as popular a label, is actually the one we most often see when we buy rubellite, paraiba (copper-bearing neons) or even watermelon varieties of tourmaline.
What causes the color in watermelon tourmaline? As the raw tourmaline crystal grows larger and thickens out, it's exposed to different elements such as manganese and lithium, which consequentially cause the gemstone to change color from a pink core through a pale zone to the outer green rind, creating the duo-color we're all familiar with.
Despite first being discovered in the state of Maine in the U.S., watermelon tourmaline can also be found in Brazil, Nigeria, Madagascar, and Afghanistan among other localities. Miners sometimes refrain from sending the rough stones off to cutting plants, as certain specimens can be worth more in their natural uncut state. This is only true for well-formed crystals that are hard to find and extract safely from their host matrix rock.
A lot of gem cutters like to 'slice' rough stones like loaves of bread, in order to fully exhibit the beautiful medley of color that makes it so unique. These tourmaline slices often become the centerpieces of pendants or earrings for designer jewelry pieces.
