By Yaĝé Enigmus
The right combinations of trace impurities in elbaite can cause the perception of unique colours that are somewhat unique or especially rare. These colours of tourmaline may have their own names, but similarly to other named tourmaline colours these names usually only describe the stones’ appearance and may not describe the tourmaline species.
When iron impurities producing predominantly blue hues (Fe2+/Fe2+-Fe3+) are present with small amounts of iron to titanium charge transfers (Fe2+-Ti4+), tourmaline may display bright blue-green colours. Depending on the amount of blue and green that is perceptible, these stones may sometimes be referred to as indicolite or may be described as “seafoam tourmaline”.
A seafoam elbaite gemstone from Alto Ligonha Region, Zambezia Province, Mozambique. Image: Gemological Institute of America
Olive Tourmaline and Lime Tourmaline
When the impurities responsible for the green of verdelite tourmaline are present alongside the manganese impurities responsible for elbaite’s yellow colour, this can result in the perception of various yellow-green colours depending on the ratio of green to yellow hues. This mixture can give stones colours ranging from olive/leaf green to bright lime green.
A lime elbaite gemstone from Nacala, Nampula Province, Mozambique. Image: Gemological Institute of America
Elbaite may display a range of green hues which are referred to as “mint tourmaline”; these include certain bright pure greens which may also be described as verdelite, light yellow-greens which border olive green, and certain blue-greens which border seafoam colours. Yellowish mint greens can be produced by a mixture of the impurities associated with elbaite’s yellow colour (Mn2+/Mn2+-Ti4+) and the impurities responsible for the green of verdelite (Fe2+/Fe2+-Ti4), with bluish mint greens being produced by a mixture of verdelite’s impurities (Fe2+/Fe2+-Ti4) and the iron impurities responsible for the blue of indicolite (Fe2+/Fe2+-Fe3+).
Mint tourmaline from Brazil. Image: Skyjems
Sunset Tourmaline and Orange Tourmaline
Elbaite may display orange colours when both the impurities responsible for red of rubellite and the impurities responsible for the yellow of canary tourmaline are present. The intensity of the orange colour is often somewhat soft and/or uneven, and in these cases such stones may be referred to as “sunset tourmaline”. In very rare instances, elbaite may exhibit a bright neon orange; stones with such colour are simply called “orange tourmaline”.
A sunset elbaite gemstone from Otjimbingwe, Erongo Region, Namibia. Image: Gemological Institute of America
Purple and violet are very rare colours for tourmaline to display, but the right mixture of trace impurities can produce these hues. When the iron impurities responsible for the blue of indicolite are present alongside the impurities responsible for the red of rubellite, then this mixture may produce the perception of purple/violet. Richly coloured stones of these hues are referred to as “siberite” in reference to Siberia, where purple elbaite crystals were first documented in detail.
Purple tourmaline from Brazil. Image: Skyjems
A single crystal of elbaite may contain different trace impurities that vary across the stone. This variation may cause a stone to display multiple distinct zones of colour. Such stones are referred to as “bi-colour tourmaline” when two hues are visible, “tri-colour tourmaline” when three hues are visible and are broadly called “polychrome tourmaline” when more than one hue is present, but the latter is most often used to describe stones showing more than three colours. The most famous colour combination in polychrome tourmaline is pink and green, affectionately referred to as “watermelon tourmaline”, although strictly speaking true watermelon tourmaline must show concentric colour zoning, where a crystal’s core shows pinks/reds and the outer layers display green hues. Polychrome tourmalines are frequently cut into gemstones that display different colours at each end, but crystals may also be sliced perpendicular to their c-axis if the stone possesses concentric zoning, a common practice with true watermelon tourmaline.
Tri-Colour Tourmaline. Image: GIA.edu
Cuprian Tourmaline (and Paraíba Tourmaline)
One of the most valuable forms of elbaite tourmaline is coloured by trace impurities of divalent copper (Cu2+), sometimes in combination with manganese (Mn2+ and/or Mn3+). Such stones may exhibit a number of different colours depending on the ratio of impurities present, and are known as “cuprian tourmaline”. Divalent copper (Cu2+) on its own produces an intense neon blue colour in elbaite, with the addition of divalent manganese producing aqua blues and neon greens, and the addition of iron to iron charge transfers (Fe2+-Fe3+) producing light sky blues; when divalent copper (Cu2+) is present alongside trivalent manganese (Mn3+) impurities, this may produce violets, pinks, and reds. In the late 1980’s, an important deposit of cuprian elbaite tourmaline was found in the Brazilian state of Paraíba which produced stones possessing very high concentrations of copper and exhibiting uniquely bright colours. The stones found in Paraíba were separated from other cuprian tourmalines with the name “Paraíba tourmaline” and this terminology has since been applied to cuprian tourmaline from other localities, although the name is sometimes used incorrectly as only stones that contain sufficient copper concentrations are considered to be true “Paraíba-type” tourmaline; unlike most other tourmaline descriptors, this name does refer to a specific species of tourmaline and is exclusively applied to copper-bearing elbaite.
Paraíba Tourmaline from Mozambique. Image: Skyjems
Elbaite accounts for the majority of tourmaline gemstones, but it is not the only tourmaline mineral that may be used in jewelry. In the last part of this series, explore the other tourmaline minerals that are sometimes used as gemstones.
Here are some examples of the beautiful tourmaline in the Skyjems collection!
© Yaĝé Enigmus