TOURMALINE INFORMATIONS

TOPIC 01: Tourmalines are gems with an incomparable variety of colours. The reason, according to an old Egyptian legend, is that the tourmaline, on its long journey up from the centre of the Earth, passed over a rainbow. In doing so, it assumed all the colours of the rainbow. And that is why it is still referred to as the 'gemstone of the rainbow' today.

The name tourmaline comes from the Singhalese words 'tura mali'. In translation, this means something like 'stone with mixed colours', referring to the colour spectrum of this gemstone, which outdoes that of all other precious stones. There are tourmalines from red to green and from blue to yellow. They often have two or more colours. There are tourmalines which change their colour when the light changes from daylight to artificial light, and some show the light effect of a cat's eye. No two tourmalines are exactly alike. This gemstone has an endless number of faces, and for that reason it suits all moods. No wonder that magical powers have been attributed to it since ancient times. In particular, it is the gemstone of love and of friendship, and is said to render them firm and long-lasting.

Colours, names and nicknames

In order to understand this variety of colour, you will have to brush up your knowledge of gemmology a little: tourmalines are mixed crystals of aluminium boron silicate with a complex and changing composition. The mineral group is a fairly complex one. Even slight changes in the composition cause completely different colours. Crystals of only a single colour are fairly rare; indeed the same crystal will often display various colours and various nuances of those colours. And the trademark of this gemstone is not only its great wealth of colour, but also its marked dichroism. Depending on the angle from which you look at it, the colour may be different or more or less intense. It is always at its most intense when viewed looking toward the main axis, a fact to which the cutter must pay great attention when lining up the cut. This gemstone has excellent wearing qualities and is easy to look after, for all tourmalines have a good hardness of 7 to 7.5 on the Mohs scale. So the tourmaline is an interesting gemstone in many ways.

TIn the trade, the individual colour variants have their own names. For example, a tourmaline of an intense red is known as a 'rubellite', but only if it continues to display the same fine ruby red in artificial light as it did in daylight. If the colour changes when the light source does, the stone is called a pink or shocking pink tourmaline. In the language of the gemmologists, blue tourmalines are known as 'indigolites', yellowish-brown to dark brown ones as 'dravites' and black ones as 'schorl'. The last mentioned, mostly used for engravings and in esotericism, is said to have special powers with which people can be protected from harmful radiation.

One particularly popular variety is the green Tourmaline, known as a 'verdelite' in the trade. However, if its fine emerald-like green is caused by tiny traces of chrome, it is referred to as a 'chrome tourmaline'. The absolute highlight among the tourmalines is the 'Paraiba tourmaline', a gemstone of an intense blue to blue-green which was not discovered until 1987 in a mine in the Brazilian state of Paraiba. In good qualities, these gemstones are much sought-after treasures today. Since tourmalines from Malawi with a vivid yellow colour, known as 'canary tourmalines', came into the trade, the colour yellow, which was previously very scarce indeed, has been very well represented in the endless spectrum of colours boasted by the 'gemstone of the rainbow'.

Yet the tourmaline has even more names: stones with two colours are known as bicoloured tourmalines, and those with more than two as multicoloured tourmalines. Slices showing a cross-section of the tourmaline crystal are also very popular because they display, in a very small area, the whole of the incomparable colour variety of this gemstone. If the centre of the slice is red and the area around it green, the stone is given the nickname 'water melon'. On the other hand, if the crystal is almost colourless and black at the ends only, it is called a 'Mohrenkopf', (resembling a certain kind of cake popular in Germany).

Tourmalines are found almost all over the world. There are major deposits in Brazil, Sri Lanka and South and south-west Africa. Other finds have been made in Nigeria, Zimbabwe, Kenya, Tanzania, Mozambique, Madagascar, Pakistan and Afghanistan. Tourmalines are also found in the USA, mainly in California and Maine. Although there are plenty of gemstone deposits which contain tourmalines, good qualities and fine colours are not often discovered among them. For this reason, the price spectrum of the tourmaline is almost as broad as that of its colour.

It is not only designers who love the tourmaline on account of its inspiring variety of colour. Scientists too are interested in it because of its astonishing physical qualities, for tourmalines can become electrically charged when they are heated and then allowed to cool. Then, they have a positive charge at one end and a negative one at the other. This is known as 'pyro-electricity', derived from the Greek word 'pyr', meaning fire. The gemstone also becomes charged under pressure, the polarity subsequently changing when the pressure is taken off. When the charge changes the tourmaline begins to oscillate, similar to a rock crystal but much more pronouncedly. The Dutch, who were the first to bring the tourmaline to Europe, were familiar with this effect a long time before it was able to be provided with a scientific explanation. They used a heated tourmaline to draw up the ash from their meerschaum pipes, and called the gemstone with the amazing powers an 'aschentrekker'.

In the fascinating world of gemstones, the tourmaline is very special. Its high availability and its glorious, incomparable colour spectrum make it one of our most popular gemstones - and apart from that, almost every tourmaline is unique.

TOPIC 02:Tourmaline is a crystal boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of colors. The name comes from the Sinhalese word "Thuramali" or "Thoramalli" , which applied to different gemstones found in Sri Lanka.

History
Brightly colored Sri Lankan gem tourmalines were brought to Europe in great quantities by the Dutch East India Company to satisfy a demand for curiosities and gems. At the time it was not realised that schorl and tourmaline were the same mineral.

Tourmaline species and varieties
Dravite species: from the Drave district of Carinthia Dark yellow to brownish black—dravite

Schorl species: Bluish or brownish black to Black—schorl

Elbaite species: named after the island of Elba, Italy Red or pinkish-red—rubellite variety (from ruby)
Dark black—schorl (from indigo)
Light blue to bluish green—Brazilian indicolite variety
Green—verdelite or Brazilian emerald variety
Colorless—achroite variety

Schorl
The most common species of tourmaline is schorl. It may account for 95% or more of all tourmaline in nature. The early history of the mineral schorl shows that the name "schorl" was in use prior to 1400 because a village known today as Zschorlau (in Saxony, Germany) was then named "Schorl" (or minor variants of this name). This village had a nearby tin mine where, in addition to cassiterite, black tourmaline was found. The first description of schorl with the name "schürl" and its occurrence (various tin mines in the Saxony Ore Mountains) was written by Johannes Mathesius (1504–1565) in 1562 under the title "Sarepta oder Bergpostill".[3] Up to about 1600, additional names used in the German language were "Schurel", "Schörle", and "Schurl". Beginning in the 18th century, the name Schörl was mainly used in the German-speaking area. In English, the names shorl and shirl were used in the 18th century. In the 19th century the names common schorl, schörl, schorl and iron tourmaline were used in the Anglo-Saxon area.[3] The word tourmaline has two etymologies, both from the Sinhalese word turamali, meaning "stone attracting ash" (a reference to its pyroelectric properties) or according to other sources "mixed gemstones".

Dravite
Black Dravite on a grey matrix
The name dravite was used for the first time by Gustav Tschermak (1836–1927), Professor of Mineralogy and Petrography at the University of Vienna, in his book Lehrbuch der Mineralogie (published in 1884) for magnesium-rich (and sodium-rich) tourmaline from the village Unterdrauburg, Drava river area, Carinthia, Austro-Hungarian Empire. Today this tourmaline locality (type locality for dravite) at the village Dravograd (near Dobrova pri Dravogradu), is a part of the Republic of Slovenia.[4] Tschermak gave this tourmaline the name dravite, for the Drava river area, which is the district along the Drava River (in German: Drau, in Latin: Drave) in Austria and Slovenia. The chemical composition which was given by Tschermak in 1884 for this dravite approximately corresponds to the formula NaMg3(Al,Mg)6B3Si6O27(OH), which is in good agreement (except for the OH content) with the endmember formula of dravite as known today.[4]

Elbaite
A lithium-tourmaline (elbaite) was one of three pegmatitic minerals from Utö, Sweden, in which the new alkali element lithium (Li) was determined in 1818 by Arfwedson for the first time.[5] Elba Island, Italy, was one of the first localities where colored and colorless Li-tourmalines were extensively chemically analysed. In 1850 Rammelsberg described fluorine (F) in tourmaline for the first time. In 1870 he proved that all varieties of tourmaline contain chemically bound water. In 1889 Scharitzer proposed the substitution of (OH) by F in red Li-tourmaline from Sušice, Czech Republic. In 1914 Vernadsky proposed the name Elbait for lithium-, sodium-, and aluminum-rich tourmaline from Elba Island, Italy, with the simplified formula (Li,Na)HAl6B2Si4O21.[5] Most likely the type material for elbaite was found at Fonte del Prete, San Piero in Campo, Campo nell'Elba, Elba Island, Livorno Province, Tuscany, Italy.[5] In 1933 Winchell published an updated formula for elbaite, H8Na2Li3Al3B6Al12Si12O62, which is commonly used to date written as Na(Li1.5Al1.5)Al6(BO3)3[Si6O18](OH)3(OH).[5] The first crystal structure determination of a Li-rich tourmaline was published in 1972 by Donnay and Barton, performed on a pink elbaite from San Diego County, California, USA.

Chemical composition of the tourmaline group
The tourmaline mineral group is chemically one of the most complicated groups of silicate minerals. Its composition varies widely because of isomorphous replacement (solid solution), and its general formula can be written as

XY3Z6(T6O18)(BO3)3V3W,

where:[6]

X = Ca, Na, K, vacancy

Y = Li, Mg, Fe2+, Mn2+, Zn, Al, Cr3+, V3+, Fe3+, Ti4+, vacancy

Z = Mg, Al, Fe3+, Cr3+, V3+

T = Si, Al, B

B = B, vacancy

V = OH, O

W = OH, F, O

Buergerite
NaFe3+3Al6Si6O18(BO3)3O3F

Chromdravite
NaMg3Cr6Si6O18(BO3)3(OH)4

Dravite
NaMg3Al6Si6O18(BO3)3(OH)4

Elbaite
Na(Li1.5,Al1.5)Al6Si6O18(BO3)3(OH)4

Feruvite
CaFe2+3(MgAl5)Si6O18(BO3)3(OH)4

Foitite
(Fe2+2Al)Al6Si6O18(BO3)3(OH)4

Liddicoatite
Ca(Li2Al)Al6Si6O18(BO3)3(OH)3F

Magnesiofoitite
(Mg2Al)Al6Si6O18(BO3)3(OH)4

Olenite
NaAl3Al6Si6O18(BO3)3O3OH

Povondraite
NaFe3+3(Fe3+4Mg2)Si6O18(BO3)3(OH)3O

Rossmanite
(LiAl2)Al6Si6O18(BO3)3(OH)4

Schorl
NaFe2+3Al6Si6O18(BO3)3(OH)4

Uvite
CaMg3(MgAl5)Si6O18(BO3)3(OH)3F

Vanadiumdravite
NaMg3V6Si6O18(BO3)3(OH)4


Crystal structure
Tourmaline belongs to the trigonal crystal system and occurs as long, slender to thick prismatic and columnar crystals that are usually triangular in cross-section. The style of termination at the ends of crystals is asymmetrical, called hemimorphism. Small slender prismatic crystals are common in a fine-grained granite called aplite, often forming radial daisy-like patterns. Tourmaline is distinguished by its three-sided prisms; no other common mineral has three sides. Prisms faces often have heavy vertical striations that produce a rounded triangular effect. Tourmaline is rarely perfectly euhedral. An exception was the fine dravite tourmalines of Yinnietharra, in western Australia. The deposit was discovered in the 1970s, but is now exhausted. All hemimorphic crystals are piezoelectric, and are often pyroelectric as well.

Color
Tourmaline gemstones - Mozambique
Tourmaline has a variety of colors. Usually, iron-rich tourmalines are black to bluish-black to deep brown, while magnesium-rich varieties are brown to yellow, and lithium-rich tourmalines are almost any color: blue, green, red, yellow, pink, etc. Rarely, it is colorless. Bi-colored and multicolored crystals are common, reflecting variations of fluid chemistry during crystallization. Crystals may be green at one end and pink at the other, or green on the outside and pink inside; this type is called watermelon tourmaline. Some forms of tourmaline are dichroic, in that they change color when viewed from different directions.

Physics explains color in terms of the wavelength of radiation. A spectrograph that only identifies the position of spectral lines will perfectly differentiate between a radiation at 0.530 µm and another at 0.532 µm, where our eyes will only perceive the same green.

The pink color of tourmalines from many fields is the result of a continued natural irradiation. During their growth, these tourmalines incorporate Mn2+, whereas initially they are by nature very pale. Their granitic environment exposes to them a natural gamma ray exposure due to radioactive decay of 40K, causing the gradual formation of the Mn3+ ions responsible for a pink to red color.[citation needed]

Treatments
Some tourmaline gems, especially pink to red colored stones, are altered by irradiation to improve their color. Irradiation is almost impossible to detect in tourmalines, and does not impact the value. Heavily-included tourmalines, such as rubellite and Brazilian paraiba, are sometimes clarity-enhanced. A clarity-enhanced tourmaline (especially paraiba) is worth much less than a non-treated gem.[7]

Geology
Tourmaline is found in granite and granite pegmatites and in metamorphic rocks such as schist and marble. Schorl and lithium-rich tourmalines are usually found in granite and granite pegmatite. Magnesium-rich tourmalines, dravites, are generally restricted to schists and marble. Tourmaline is a durable mineral and can be found in minor amounts as grains in sandstone and conglomerate, and is part of the ZTR index for highly-weathered sediments.

Tourmaline localities

Gem and specimen tourmaline is mined chiefly in Brazil and Africa. Some placer material suitable for gem use comes from Sri Lanka. In addition to Brazil, tourmaline is mined in Tanzania, Nigeria, Kenya, Madagascar, Mozambique, Namibia, Afghanistan, Pakistan, Sri Lanka, and Malawi.[8]

United States
Some fine gems and specimen material has been produced in the United States, with the first discoveries in 1822, in the state of Maine. California became a large producer of tourmaline in the early 1900s. The Maine deposits tend to produce crystals in raspberry pink-red as well as minty greens. The California deposits are known for bright pinks, as well as bicolors. During the early 1900s, Maine and California were the world's largest producers of gem tourmalines. The Empress Dowager Tz'u Hsi of China loved pink tourmaline and bought large quantities for gemstones and carvings from the then new Himalaya Mine, located in San Diego County, California.[9] It is not clear when the first tourmaline was found in California. Native Americans have used pink and green tourmaline as funeral gifts for centuries. The first documented case was in 1890 when Charles Russel Orcutt found pink tourmaline at what later became the Stewart Mine at Pala, San Diego.[10]

Brazil
Watermelon Tourmaline mineral on quartz matrix (crystal approximately 2 cm wide at face)
Almost every color of tourmaline can be found in Brazil, especially in the Brazilian states of Minas Gerais and Bahia. In 1989, miners discovered a unique and brightly colored variety of tourmaline in the state of Paraíba. The new type of tourmaline, which soon became known as paraiba tourmaline, came in unusually vivid blues and greens. These colors were often described as "neon" since they appeared to glow. Brazilian paraiba tourmaline is usually heavily included. Much of the paraiba tourmaline from Brazil actually comes from the neighboring state of Rio Grande do Norte. Material from Rio Grande do Norte is often somewhat less intense in color, but many fine gems are found there. It was determined that the element copper was important in the coloration of the stone.

Africa
In the late 1990s, copper-containing tourmaline was found in Nigeria. The material was generally paler and less saturated than the Brazilian materials, although the material generally was much less included. A more recent African discovery from Mozambique has also produced beautiful tourmaline colored by copper, similar to the Brazilian paraiba. While its colors are somewhat less bright than top Brazilian material, Mozambique paraiba is often less included and has been found in larger sizes. The Mozambique paraiba material usually is more intensely colored than the Nigerian. There is a significant overlap in color and clarity with Mozambique paraiba and Brazilian paraiba, especially with the material from Rio Grande do Norte. While less expensive than top quality Brazilian paraiba, some Mozambique material sells for well over $5,000 per carat, which still is extremely high compared to other tourmalines.

Tourmaline mineral (approximately 10 cm tall)
Another highly valuable variety is chrome tourmaline, a rare type of dravite tourmaline from Tanzania. Chrome tourmaline is a rich green color due to the presence of chromium atoms in the crystal; chromium also produces the green color of emeralds. Of the standard elbaite colors, blue indicolite gems are typically the most valuable, followed by green verdelite and pink to red rubellite.[citation needed] There are also yellow tourmalines, sometimes known as canary tourmaline. Zambia is rich in both red and yellow tourmaline, which are relatively inexpensive in that country. Ironically the rarest variety, colorless achroite, is not appreciated and is the least expensive of the transparent tourmalines.

Afghanistan

Extra fine indicolite (blue tourmaline) and verdelite (green tourmaline) are found in the Nuristan region (Ghazi Abad district) and Pech Valley (Pech and Chapa Dara districts) of Kunar province. Gem-quality tourmalines are faceted (cut) from 0.50–10 gram sizes and have unusually high clarity and intense shades of color.