Watermelon Tourmaline: What Is Watermelon Tourmaline

Watermelon Tourmaline is a variety of tourmaline that is characterized by its pink or red center and green exterior. It is named for its resemblance to a watermelon slice. Watermelon Tourmaline is a rare and valuable gemstone, and it is often used in jewelry.

Watermelon Tourmaline is a hard gemstone, with a Mohs hardness of 7 to 7.5. This means that it is relatively resistant to scratching. Watermelon Tourmaline is also a relatively stable gemstone, and it is not easily affected by heat or chemicals.

All colored Tourmaline gems display pleochroism, meaning their color changes when viewed at different angles. In some Tourmaline gems, this effect is hardly noticeable, while in others it is strongly apparent. Gemstone cutters must take this into account when cutting a Tourmaline, so that the finished gem brings out its best color.

Watermelon Tourmaline is found in a few locations around the world, but the most important source is the state of Minas Gerais in Brazil. Watermelon Tourmaline can also be found in Nigeria, Madagascar, Afghanistan, Sri Lanka, Australia, and the United States.

What does watermelon tourmaline look like

As the name suggests, watermelon tourmaline displays banded colours that resemble a ripe slice of watermelon. The red or pink centre is surrounded by a rim of green, often separated by a sliver of pale pink or white. The brightly coloured zones can also occur at either end of the gem although there is some debate as to whether these stones should be classified as watermelon or simply bi-colour tourmalines.

Watermelon Tourmaline: What Is Watermelon Tourmaline.
A slice of watermelon tourmaline

Watermelon tourmaline crystals tend to form with a distinctive rounded triangular shape, as demonstrated beautifully in this stunning pendant by Paula Crevoshay. Watermelon tourmalines with vivid, clearly separated colours are very rare and command high prices. Matthew Morrell says: “Clean stones with good crystal in the 4-7 carats range, with an even distribution of each colour, change hands in Europe at between $500-$600 per carat.”

Cutting the stone into slices like a loaf of bread rather than faceting the rough often enhances the resemblance to a real watermelon. Their complex structure makes tourmalines very difficult to cut. A great deal of expertise is required to identify areas of tension within the stone, which can cause it to crack during the cutting process.

What causes watermelon tourmaline colours

The bi-coloured and multi-coloured 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 coloured zones across the length of the crystal, or they can have a core of one colour and an outer edge of another colour. A single tourmaline crystal can contain up to 15 different colours 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 colour 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 colour from a pink centre through a pale zone to the green rind.

A slice of watermelon tourmaline

Watermelon Tourmaline Properties

Color: Concentrically zoned with a pink-red core and a green exterior. The intensity and shades of both colors can vary greatly, ranging from pale blush pink and light green to vivid raspberry red and deep emerald green.

Luster: Vitreous to sub-vitreous, meaning glassy with a slightly waxy or greasy appearance.

Streak: White.

Hardness: 7-7.5 on the Mohs scale, making it durable enough for everyday wear in jewelry.

Cleavage: Imperfect to good basal cleavage, meaning it tends to break along certain planes. Careful cutting and polishing are needed to avoid fractures.

Crystal Form: Hexagonal prisms and striated columns, often elongated and tapering to a point.

Density: 3.02-3.22 g/cm³, relatively heavy for its size due to the presence of various elements in its composition.

Transparency: Can be transparent, translucent, or opaque. Gem-quality watermelon tourmaline is usually translucent to transparent, allowing light to play through the contrasting colors.

Fracture: Conchoidal, meaning it breaks with smooth, curved surfaces.

Solubility: Insoluble in common acids and water.

Magnetism: Non-magnetic.

Fluorescence: Inert, meaning it does not glow under ultraviolet light.

Pleochroism: Slight pleochroism can be observed, especially in the green areas, where the color appears slightly different depending on the viewing angle.

Refractive Index: 1.603 - 1.655, relatively high compared to other gemstones, contributing to its brilliance and sparkle.