How Does Watermelon Tourmaline Form?

Rough tourmaline crystals form in elongated shapes underground. To be a true “watermelon,” this crystal should have a pink or red core with a green rind. The pink or red center of these crystals forms first. Then, a shift in chemistry in the geothermal fluid that creates the crystal occurs. Instead of manganese, which causes the pink color, iron enters the solution, which imparts a green hue to the crystal.

While bi-color and parti-color tourmalines with color transitions along the longer axis of the crystal also form, these aren’t considered watermelon tourmaline. Nonetheless, some dealers refer to any bi-color pink and green tourmalines as watermelon tourmaline.

Watermelon Tourmaline Buying and the Four Cs

The IGS tourmaline value listing has price guidelines for tourmalines.

Color

By far, the most important criterion for assessing the value of watermelon tourmaline is color. Traditionally, this gem has a pink center with a ring of green around the edge. Sometimes, a colorless ring separates these colors. “Reverse” watermelon tourmalines, with a green core and pink edge, also occur. In addition, because tourmalines can form in any color of the rainbow, other color combinations may occur. While these aren’t traditional…