Rubellite - Paprok Mine Afghanistan, Elbaite - San Piero in Campo Italy, Paraiba Tourmaline - Paraiba Brazil Image Credits - CC Géry PARENT CC BY-SA 3.0, Didier Descouens CC BY-SA 4.0, The Assay House
Few minerals rival tourmaline for sheer diversity of colour and complexity of composition. Tourmaline is not a single mineral but a large family of closely related borosilicate minerals with a general chemical formula of XY₃Z₆(T₆O₁₈)(BO₃)₃V₃W, where numerous elements may substitute for one another. This flexible atomic structure accounts for tourmaline’s exceptional variety in hue and form. Despite these chemical differences, all species share the same basic hexagonal (trigonal) crystal system, often forming long, striated prisms with well-defined terminations.
Mineralogists and collectors have been interested in tourmaline's complexity for hundreds of years. Its structure is composed of rings of six linked silicate tetrahedra (Si₆O₁₈) running parallel to the crystal’s long axis, creating channels where cations such as lithium, sodium, calcium, and iron can reside. These substitutions profoundly influence colour, density, and even magnetic properties. The presence of boron, a defining component, gives tourmaline its unique stability and contributes to its characteristic pyroelectric and piezoelectric effects – it can generate an electric charge when heated or compressed.
Among the many species, three dominate gem and specimen collections: schorl, dravite, and elbaite. They are also the most commonly occurring tourmalines:
Schorl is the most abundant variety, rich in iron and usually black, brown or dark grey with a resinous lustre. It forms in granitic pegmatites and metamorphic rocks worldwide and often appears as lustrous prismatic crystals. Schorl is found in large deposits in Erongo, Namibia; the Ural Mountains of Russia; Andalusia, Spain; and the pegmatite fields of Maine, Connecticut and California in the USA.
Dravite is a sodium–magnesium tourmaline, which tends to be green or brown and often translucent. Its lack of iron gives it a softer colour and a lighter tone. Excellent specimens come from the metamorphosed rocks of the Merelani Hills in Tanzania, as well as Brazil, Australia, and New York State, USA.
Elbaite is a lithium-aluminium variety of tourmaline that is by far the most colourful and desirable among collectors and gemologists alike. When its pink core is surrounded by green outer zones, the mineral forms the highly sought-after 'watermelon' tourmaline. Elbaite was first identified on the island of Elba, Italy, and today fine examples come from Brazil’s Minas Gerais, Afghanistan’s Nuristan Province, Madagascar, and the San Diego County pegmatites in California.
Siberite is a very rare, red-violet variety of elbaite originating from Siberia. It often occurs in sizeable crystals with an almost spherical form.
Tourmaline’s variety extends beyond these three principal species to a significant number of rarer minerals.
Uvite is a rare calcium–magnesium tourmaline, known for its brown, black or deep green crystals, found in Brumado, Brazil, in New York State, USA, and in Livorno, Italy.
Liddicoatite is a type of lithium-aluminium tourmaline also rich in calcium. The species is renowned for its complex internal colour zoning and vibrant hues, particularly those from Tsitondroina, Madagascar. The zones can feature shades of purple, pink, green, blue, and yellow. The most prized specimens display a distinct triangular colour pattern resembling the 'Mercedes' star.
Achroite is a rare, colourless form of tourmaline. It's the scarcest of all tourmaline varieties and is prized for special industrial purposes. The most aesthetic specimens come from Nuristan in Afghanistan and the Skardu region of Pakistan.
Rubellite is the most valuable variety of tourmaline, admired for its vivid red and pink hues produced by traces of iron and manganese. Striking examples come from the Jonas Mine, Minas Gerais, in Brazil, and the Himalaya Mine, California, USA.
Indicolite is a blue to greenish-blue tourmaline variety, highly sought after for jewellery. Its shades can vary from delicate light blue to rich deep teal, depending on the amount of iron content. Striking specimens come from Nuristan in Afghanistan and the Otjua Mine, Erongo, Namibia.
Chrome-Tourmaline is a striking dark-green variety of tourmaline whose intense colour is caused by the presence of chromium. Superb, water-clear specimens come from the Merelani Hills in Tanzania and Haute-Garonne in France.
Verdelite is also a green form of tourmaline, ranging from pale grassy tones to dark forest hues. The colour results from the presence of iron and titanium, and it is more common than chrome tourmaline. Probably the best-known examples come from the Santa Rosa mine, Itambacuri, Minas Gerais, Brazil.
Other rare members, including foitite, povondraite, and fluor-dravite, reveal subtle changes in chemistry that define distinct mineral species within the tourmaline group.
Although it is not a distinct species, the term "watermelon tourmaline" is used to describe specimens, most commonly elbaite, that feature a pink or red core surrounded by a green outer layer, resembling the appearance of a watermelon slice. "Bi-colour tourmaline" is used to describe specimens that feature two distinct colours within a single crystal, commonly in contrasting combinations, such as green and pink or blue and yellow. "Multicolour tourmaline" is used to describe specimens that exhibit three or more clearly defined colours, often arranged in beautiful natural zoning patterns. Finally, "Paraíba tourmaline" is a rare and highly prized variety known for its electrifying blue-green glow, which is caused by the presence of copper and manganese.
Physically, tourmaline is admired not only for its colour but also for its optical and electrical behaviour. Many varieties exhibit strong pleochroism, which means they display different colours when viewed from different directions. This, combined with their vibrant tones and excellent hardness of 7–7.5 on the Mohs scale, makes tourmaline ideal for both jewellery and mineral collections.
Tourmaline’s occurrence is global, yet its finest gemstone sources are concentrated in Brazil, Afghanistan, Mozambique, Nigeria, Madagascar, and the United States. The Maine and California pegmatites have produced world-class gem crystals since the 19th century, while African deposits continue to yield extraordinary rubellite and indicolite specimens.
Few species in the world of minerals captivate the imagination like tourmaline. Its endless colour palette, chemical complexity, and worldwide distribution make it a true natural marvel – a kaleidoscope of Earth’s geological creativity. From the black depths of schorl to the pink-green glow of watermelon tourmaline, each crystal embodies a story of elemental harmony frozen in stone.
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