Tourmaline
Tourmaline was once nicknamed the Ceylonese Magnet. The gem could attract hot ashes and then push them away again, a trick that came from its pyroelectric properties. Behind that curiosity sits a crystalline silicate mineral group in which boron joins elements such as aluminium, iron, magnesium, sodium, lithium or potassium. The result is a gemstone that appears in a wide variety of colors. Why does one mineral family carry so many different names? How can a single crystal be green at one end and pink at the other? Why do some tourmalines answer to a magnet while others ignore it entirely? And how did a gem from the mines of a Saxon village and the shores of Sri Lanka end up at the center of a modern gem rush in Brazil and Africa?
The word tourmaline comes from tōramalli, a Sinhalese term that referred to carnelian gemstones. Brightly colored gems from Ceylon reached Europe in great quantities aboard ships of the Dutch East India Company, which was feeding a demand for curiosities and gems.
A far older name belongs to schorl, the brownish-black to black species. It was already in use before 1400, when the village known today as Zschorlau in Saxony, Germany, went by Schorl or a close variant. A nearby tin mine produced black tourmaline alongside cassiterite.
In 1562 Johannes Mathesius, who lived from 1504 to 1565, wrote the first description of the mineral. He spelled it schürl and placed it in various tin mines of the Ore Mountains. His work was titled Sarepta oder Bergpostill. Until about 1600 German writers also used Schurel, Schörle and Schurl. From the 18th century, Schörl dominated in German-speaking regions, while English writers of that century used shorl and shirl. By the 19th century, common schorl and iron tourmaline were the English terms.
Dravite arrived much later. In his 1884 book Lehrbuch der Mineralogie, Gustav Tschermak, professor of mineralogy and petrography at the University of Vienna, used the name for magnesium-rich and sodium-rich tourmaline from the village of Dobrova, near Unterdrauburg. He took it from the Drava river district, called Drau in German and Drave in Latin, which runs through Austria and Slovenia. Dobrova, near Dravograd, was then in Carinthia in the Austro-Hungarian Empire. Today it lies in the Republic of Slovenia and is the type locality for dravite.
The formula Tschermak reported in 1884 matches the modern endmember formula closely, apart from the hydroxyl content.
In 1818 the chemist Johan August Arfwedson identified the alkali element lithium for the first time. He found it in three pegmatitic minerals from Utö, Sweden, and a lithium tourmaline later named elbaite was one of them. Elba Island, Italy, became one of the first places where colored and colorless lithium tourmalines were extensively analysed.
Karl Friedrich August Rammelsberg described fluorine in tourmaline for the first time in 1850. In 1870 he proved that all varieties of tourmaline contain chemically bound water. In 1889 a researcher named Scharitzer suggested that fluorine can substitute for hydroxyl in red lithium tourmaline from Sušice in the Czech Republic.
In 1914 Vladimir Vernadsky proposed the name Elbait for lithium-, sodium- and aluminum-rich tourmaline from Elba Island. The type material most likely came from Fonte del Prete, San Piero in Campo, Campo nell'Elba, in the Province of Livorno, Tuscany. Winchell published an updated formula in 1933. In 1972 Donnay and Barton published the first crystal structure of a lithium-rich tourmaline, working on a pink elbaite from San Diego County, California.
The group is chemically one of the most complicated among silicate minerals. Isomorphous replacement, also called solid solution, lets the composition vary widely, and the general formula is written XY3Z6(T6O18)(BO3)3V3W. The X position can hold calcium, sodium, potassium or a vacancy. The V position holds hydroxyl or oxygen, and the W position holds hydroxyl, fluorine or oxygen.
The International Mineralogical Association recognizes 42 minerals in the group, from adachiite and bosiite to darrellhenryite and ertlite. Species named before the association was founded in 1958 have no IMA number. The commission published approved symbols for each species in 2021, after a revised nomenclature appeared in 2011.
All of that variety grows from one architectural plan, which starts with a ring of six silica units.
Only one common mineral grows prisms with three sides, and that mineral is tourmaline. Its crystals range from long and slender to thick and columnar, usually triangular in cross-section. The faces are often curved and heavily striated, which gives a rounded triangular effect.
Tourmaline is a six-member ring cyclosilicate in the trigonal crystal system. Small slender crystals are common in aplite, a fine-grained granite, where they often form radial, daisy-like patterns. Perfectly euhedral crystals are rare. The fine dravite tourmalines of Yinnietharra, in western Australia, were an exception. That deposit was discovered in the 1970s and is now exhausted.
Some crystals end in asymmetrical terminations, a feature called hemimorphism. Every hemimorphic crystal is piezoelectric, and many are pyroelectric as well. This is the property behind the old trick with hot ashes.
Inside, a silica ring of six units binds above to a large cation such as sodium. Below, the ring binds to a layer of metal ions and hydroxyls or halogens, which resembles a fragment of kaolin. That layer in turn binds to three triangular borate ions. Units joined end to end form columns that run the length of the crystal.
Each column links with two others, offset by one-third and two-thirds of the height of a single unit. Together they form bundles of three, and the bundles pack to build the crystal. Because neighboring columns are offset, the basic structural unit is not a unit cell. The true unit cell includes parts of several units from adjacent columns.
Chemists in the 19th century put this geometry to work, shining rays onto a cut and polished surface of the gem to polarize light.
Iron-rich tourmalines are usually black, bluish-black or deep brown. Magnesium-rich varieties run from brown to yellow. Lithium-rich tourmalines can be almost any color, including blue, green, red, yellow and pink, and they are only rarely colorless.
The elbaite species carries the best-known color names. Red or pinkish-red stones are rubellite. Light blue to bluish-green stones are indicolite, a name taken from indigo. Green stones are verdelite, and the colorless ones are achroite.
In India, green tourmaline is especially popular because of its association with Vedic astrology.
Bi-colored and multicolored crystals are common, because the chemistry of the fluid changes as a crystal grows. A crystal may be green at one end and pink at the other, or green outside and pink inside. This type is called watermelon tourmaline and is prized in jewelry. A brooch made in 1969 by the British designer Andrew Grima, born in Italy and living from 1921 to 2007, shows it well. It combines gold, watermelon tourmaline and diamonds. It belongs to the collection of Kimberly Klosterman and has been displayed at the Cincinnati Art Museum.
Some forms of tourmaline are dichroic, meaning they change color when viewed from different directions.
The pink of many tourmalines is the work of time and radiation. As these crystals grew, they took in Mn2+ ions and were at first very pale. Natural gamma rays from the radioactive decay of 40K in the surrounding granite slowly formed Mn3+ ions. Those ions deepen the pink toward red.
A handheld neodymium magnet can sort some tourmaline gems from others. Opaque black schorl and yellow tsilaisite are idiochromatic, meaning their color comes from their own composition. They have high magnetic susceptibility because of their iron and manganese respectively. Most gem-quality tourmalines are elbaite, which is allochromatic. It draws most of its color and magnetic susceptibility from schorl, which imparts iron, and tsilaisite, which imparts manganese.
Among elbaites, red and pink stones have the lowest magnetic susceptibility. Bright yellow, green and blue stones are the most magnetic. Dravites such as green chromium dravite and brown dravite are diamagnetic. Blue indicolite is the only blue gemstone of any kind that shows a drag response to a neodymium magnet. A blue tourmaline that does not respond is a paraiba.
Heat treatment is common for pink to red stones. Overly dark red stones can be lightened with careful heating. In manganese-bearing stones that are near-colorless or pale pink, gamma-rays or electron beams can greatly increase the pink. Irradiation is almost impossible to detect in tourmaline and does not currently affect value.
Heavily included stones, such as rubellite and Brazilian paraiba, are sometimes clarity-enhanced. A clarity-enhanced paraiba is worth much less than an untreated gem of equal clarity, which explains why the variety draws so much scrutiny.
Schorl may account for 95% or more of all tourmaline in nature. It is the sodium iron endmember and the most common species. Schorl and lithium-rich tourmalines usually form in granite and granite pegmatite. Dravites are generally restricted to schist and marble. Tourmaline is durable enough to survive as minor grains in sandstone and conglomerate, and it is part of the ZTR index for highly weathered sediments.
In 1821 two college students found tourmaline on Mount Mica in Paris, Maine. It was the first discovery of the gem in the United States. In 1972 miners excavating the Dunton Quarry on Plumbago Mountain in Newry opened a cavity called The Big Pocket, or The Big Find. It held two metric tons of tourmaline, including green, red and watermelon specimens. The find revived gem mining in the state.
In 2022 the Maine Mineral & Gem Museum in Bethel opened an exhibition called The Big Find: The Legend Continues. It showed stones from the 1972 find cut by 12 jewelers from across the country. Notable Maine stones include a flawless 256-carat blue gem and a 69-carat gem bought by Tiffany & Co. Maine deposits tend to give raspberry pink-red crystals and minty greens.
California is known for bright pinks and bicolors. It became a large producer in the early 1900s, and with Maine it was then one of the world's largest sources of gem tourmaline. The Empress Dowager Cixi of China loved pink tourmaline. She bought large quantities for gemstones and carvings from the then new Himalaya Mine in San Diego County.
The true first find in California is unclear. Native Americans have used pink and green tourmaline as funeral gifts for centuries. The first documented case dates to 1890, when Charles Russel Orcutt found pink tourmaline at the site that later became the Stewart Mine at Pala.
Most gem and specimen tourmaline today comes from Brazil and from Africa, including Tanzania, Nigeria, Kenya, Madagascar, Mozambique, Malawi and Namibia. Mining also takes place in Pakistan, Afghanistan and Indonesia, and in Sri Lanka and India, where some placer deposits yield gem material.
Brazil produces almost every color, especially in Minas Gerais and Bahia. A new type of blue and green tourmaline from there soon became known as paraiba. Brazilian paraiba usually contains abundant inclusions. Much of it does not actually come from the state of Paraíba but from the neighboring state of Rio Grande do Norte. Stones from Rio Grande do Norte are often somewhat less intense in color, though many fine gems come from there. Researchers determined that copper was important in the coloring of the stone.
A bluish-green paraiba measuring 36.44 x 33.75 x 21.85 mm and weighing 191.87 carat is the world's largest cut tourmaline. It is owned by Billionaire Business Enterprises and was presented in Montreal, Quebec, Canada, on the 14th of October 2009.
In the late 1990s, copper-containing tourmaline turned up in Nigeria. It was generally paler and less saturated than the Brazilian stones, though much less included. A later discovery in Mozambique also yields copper-colored tourmaline. It tends to be more intensely colored than the Nigerian material and resembles Brazilian paraiba in color. Prices are relatively lower, with better clarity and larger sizes, though pricing has risen significantly in recent years.
Tanzania offers another highly valuable variety, chrome tourmaline, a rare type of dravite. Its rich green comes from chromium atoms in the crystal. Among the standard elbaite colors, blue indicolite is typically the most valuable, followed by green verdelite and then pink to red rubellite.
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Common questions
What does the name tourmaline mean?
The name tourmaline comes from the Sinhalese word tōramalli, which referred to carnelian gemstones. Brightly colored Ceylonese tourmalines reached Europe in great quantities through the Dutch East India Company.
What is tourmaline made of?
Tourmaline is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium or potassium. The International Mineralogical Association recognizes 42 minerals in the group.
What is the most common type of tourmaline?
Schorl is the most common tourmaline species, the sodium iron endmember of the group. It may account for 95% or more of all tourmaline in nature.
Why was tourmaline called the Ceylonese Magnet?
Tourmaline was called the Ceylonese Magnet because it could attract and then repel hot ashes. This behavior comes from its pyroelectric properties.
What gives pink tourmaline its color?
Pink tourmaline gets its color from manganese. Crystals took in Mn2+ while growing, and natural gamma rays from the decay of 40K in granite slowly formed Mn3+ ions that deepen the pink to red.
What is paraiba tourmaline and where is it found?
Paraiba tourmaline is a blue to green variety colored by copper. It was first found in Brazil, much of it in Rio Grande do Norte, and later in Nigeria in the late 1990s and in Mozambique.
Where was tourmaline first found in the United States?
Tourmaline was first found in the United States in 1821, when two college students discovered it on Mount Mica in Paris, Maine. A 1972 find at Dunton Quarry in Newry produced two metric tons of tourmaline.
How can a magnet identify tourmaline?
A neodymium magnet can separate some tourmalines because iron- and manganese-rich types are magnetic. Blue indicolite is the only blue gemstone that shows a drag response, while a blue tourmaline that does not respond is paraiba.
All sources
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