Tourmalines come in a wide variety of different colors. In fact, tourmaline has one of the widest color ranges of any gemstone species, occurring in various shades of virtually every hue.
This is the part 1 of a two part post on tourmalines, one of October’s birthstones.
Irene Neuwirth’s 18K yellow gold, watermelon tourmaline and diamond ring. Photo courtesy of Irene Neuwirth.
In this post, let’s talk about watermelon tourmalines! The watermelon tourmaline is aptly named as it’s coloring mimics the rind and flesh of a watermelon! Watermelon tourmaline is pink in the center and green or green/blue around the outside. Crystals of this material are typically cut in slices to display this special arrangement.
All gems in the tourmaline family are mixed crystals of aluminum boron silicate that also contain elements such as iron, manganese, sodium, lithium or potassium. Tourmaline was first discovered in Brazil in 1554 by Francisco Spinoza. He recorded that he had found the first “Brazilian emerald.” While Brazil has lots of emeralds, he really found the first recorded green tourmaline crystal. Tourmaline’s crystals were often confused with emerald and it was not until the 19th century that the gem was classified as tourmaline.
EF Collection’s 14k rose gold, watermelon tourmaline and diamond pendant. Photo courtesy of EF Collection.
A tourmaline’s chemical composition directly influences its physical properties and is responsible for its color. Tourmalines make up a group of closely related mineral species that share the same crystal structure but have different chemical and physical properties. They share the elements silicon, aluminum, and boron, but contain a complex mixture of other elements such as sodium, lithium, calcium, magnesium, manganese, iron, chromium, vanadium, fluorine, and sometimes copper. Gemologists use a tourmaline’s properties and chemical composition to define its species. The major tourmaline species are elbaite, liddicoatite, dravite, uvite, and schorl.
Most gem tourmalines are elbaites, which are rich in sodium, lithium, aluminum, and sometimes—but very rarely—copper. They occur in granite containing pegmatites, which are rare igneous rocks. Pegmatites are sometimes rich in exotic elements that are important for the formation of certain gem minerals. Pegmatites might contain very large crystals up to 1 meter (about 3 feet) in length. Because of the nature of pegmatites, different gem pockets within one pegmatite body can hold tourmaline crystals of very different colors. Or one pocket can produce a variety of differently colored tourmalines. As a result, many mines produce a variety of gem colors.
The bi-colored and multi-colored zoning that we so often see in tourmaline gems happens when the trace elements change in concentration or composition during a crystal’s growth. These unique gems can have colored zones across the length of the crystal, or they can have a core of one color and an outer edge of another color. A single tourmaline crystal can contain up to 15 different colors or shades – no wonder it has been nicknamed the “Rainbow Gem”.
In watermelon tourmaline, pink and green Elbaite crystals are found in the same stone, and these color zones provide a visual record of its formation process. As the watermelon tourmaline crystal grows and thickens, it is exposed to different minerals such as manganese and lithium, which cause the gem to change color from a pink centre through a pale zone to the green rind.
Lydia Courteille’s 18K gold, garnet, watermelon tourmaline, and diamond brooch. Photo courtesy of W Magazine.
Leviev’s 18k white gold carved watermelon tourmaline and diamond ring. Photo courtesy of Leviev.
Elbaite, is the name given to the brightly colored members of the family. The red or pink tourmalines are know as rubellites, the blue variety are called indicolite and the highly coveted, electric blue variety are called paraiba. The watermelon tourmaline is also a Elbaite. Tourmaline has a Moh’s scale hardness of 7-7.5, which makes it a pretty durable stone for jewelry.
The confusion about the stone’s identity is even reflected in its name, which comes from toramalli, which means “mixed gems” in Sinhalese. It’s a term Dutch merchants applied to the multicolored, water-worn pebbles that miners found in the gem gravels of Ceylon (now Sri Lanka). As we discussed, a watermelon tourmaline refers to the color combination that so resembles the watermelon fruit.
Jacquie Aiche 14K gold, watermelon tourmaline slice, and diamond cuff bracelet. Photo courtesy of Jacquie Aiche.
Brazil, Nigeria, Madagascar, Afghanistan and the United States all produce watermelon tourmalines. The North American state of Maine, where the gem was first discovered at a mine in Newry in 1902, is renowned for its stunning watermelon tourmaline. In the early 1970s, a large pocket of some of the finest watermelon tourmalines ever seen was unearthed at the nearby Plumbago Gem Pit.
Do you own a watermelon tourmaline? I am always on the look out for either a unique gemstone or a piece of jewelry.