How Do Tourmalines Form?

What is Tourmaline?

In Sri Lanka, the island famous for its sapphire, chrysoberyl, and so much more gem wealth, turamali is the Sinhalese word for “stone of mixed color.” Indeed, there’s no better way to describe tourmaline. Minerals in the tourmaline group can occur in any color of the rainbow, and jewelers often use them to imitate other gemstones.

In terms of chemistry, tourmalines are sometimes called a “kitchen sink” mineral because of the wide variety of elements they may contain. The basic mineral formula is XY₃Z₆(T₆O₁₈)(BO₃)₃V₃W, where X, Y, Z, T, V, and W could represent different elements. Because of the wide variety of possible substitutions, there is a large and growing list of end-member tourmaline minerals as well as countless intermediate compositions.

Still, relatively few types of tourmaline make nice gemstones. Most tourmalines in jewelry consist of the mineral elbaite. Dravite, uvite, and schorl might also be used as gemstones, though this is less common.

Where do Tourmalines Form?

Tourmalines form in igneous and metamorphic rocks, but most gem-quality tourmaline forms in pegmatites. Pegmatites are igneous rocks that form during the last…