![Tourmaline gisements](https://upload.wikimedia.org/wikipedia/commons/a/ab/Tourmaline_gisements.jpg)
Tourmaline ( ) is a
crystalline
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosc ...
silicate
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...
mineral group In geology and mineralogy, a mineral group is a set of mineral species with essentially the same crystal structure and composed of chemically similar elements.Stuart J. Mills, Frédéric Hatert, Ernest H. Nickel, and Giovanni Ferraris (2009): "The ...
in which
boron
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
is compounded with elements such as
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
,
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
,
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
,
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
,
lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
, or
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
. Tourmaline is a
gemstone
A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...
and can be found in a wide variety of colors.
The term is derived from the
Sinhalese
Sinhala may refer to:
* Something of or related to the Sinhalese people of Sri Lanka
* Sinhalese people
* Sinhala language, one of the three official languages used in Sri Lanka
* Sinhala script, a writing system for the Sinhala language
** Sinha ...
"tōramalli", which refers to the
carnelian
Carnelian (also spelled cornelian) is a brownish-red mineral commonly used as a semi-precious gemstone. Similar to carnelian is sard, which is generally harder and darker (the difference is not rigidly defined, and the two names are often use ...
gemstones.
History
Brightly colored
Ceylon
Sri Lanka (, ; si, ශ්රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
ese gem tourmalines were brought to Europe in great quantities by the
Dutch East India Company
The United East India Company ( nl, Verenigde Oostindische Compagnie, the VOC) was a chartered company established on the 20th March 1602 by the States General of the Netherlands amalgamating existing companies into the first joint-stock ...
to satisfy a demand for curiosities and gems. Tourmaline was sometimes called the "Ceylonese Magnet" because it could attract and then repel hot ashes due to its
pyroelectric
Pyroelectricity (from the two Greek words ''pyr'' meaning fire, and electricity) is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the a ...
properties.
Tourmalines were used by chemists in the 19th century to polarize light by shining rays onto a cut and polished surface of the gem.
Species and varieties
Commonly encountered species and varieties:
Schorl species:
: Brownish black to black—''schorl'',
Dravite species: from the Drave district of
Carinthia
Carinthia (german: Kärnten ; sl, Koroška ) is the southernmost States of Austria, Austrian state, in the Eastern Alps, and is noted for its mountains and lakes. The main language is German language, German. Its regional dialects belong to t ...
: Dark yellow to brownish black—''dravite'',
Elbaite
Elbaite, a sodium, lithium, aluminium boro-silicate, with the chemical composition Na(Li1.5Al1.5)Al6Si6O18(BO3)3(OH)4, is a mineral species belonging to the six-member ring cyclosilicate tourmaline group.
Elbaite forms three series, with dravite, ...
species: named after the island of
Elba
Elba ( it, isola d'Elba, ; la, Ilva) is a Mediterranean island in Tuscany, Italy, from the coastal town of Piombino on the Italian mainland, and the largest island of the Tuscan Archipelago. It is also part of the Arcipelago Toscano National ...
,
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
: Red or pinkish-red—''
rubellite
Rubellite is the red or pink variety of tourmaline and is a member of elbaite. Rubellite is also the rarest gem in its gem family. It is occasionally mistaken for ruby. These gems typically contain inclusions.
Notable places where rubellite ca ...
'' variety,
: Light blue to bluish green— ''indicolite'' variety (from
indigo
Indigo is a deep color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the ancient dye of the same name. The word "indigo" comes from the Latin word ''indicum'', m ...
),
: Green—''verdelite'' or
emerald
Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium.Hurlbut, Cornelius S. Jr. and Kammerling, Robert C. (1991) ''Gemology'', John Wiley & Sons, New York, p ...
variety,
: Colorless—''achroite'' variety (from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
"άχρωμος" meaning "colorless").
Schorl
![Tourmaline noire ou Schorl](https://upload.wikimedia.org/wikipedia/commons/2/22/Tourmaline_noire_ou_Schorl.jpg)
The most common species of tourmaline is ''schorl'', the sodium iron (divalent) endmember of the group. 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
Zschorlau () is a community in the district of Erzgebirgskreis in Saxony, Germany.
Geography
Location
Zschorlau lies nestled in the gentle hills in the western Ore Mountains some 5 km from Aue and is overhung in the south by the ''Ste ...
(in
Saxony
Saxony (german: Sachsen ; Upper Saxon: ''Saggsn''; hsb, Sakska), officially the Free State of Saxony (german: Freistaat Sachsen, links=no ; Upper Saxon: ''Freischdaad Saggsn''; hsb, Swobodny stat Sakska, links=no), is a landlocked state of ...
, Germany) was then named "Schorl" (or minor variants of this name), and the village had a nearby
tin
Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal.
Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
mine where, in addition to
cassiterite
Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains t ...
, black tourmaline was found. The first description of schorl with the name "schürl" and its occurrence (various tin mines in the
Ore Mountains) was written by
Johannes Mathesius
Johannes Mathesius (June 24, 1504 – October 7, 1565), also called Johann Mathesius or John Mathesius, was a German minister and a Lutheran reformer. He is best known for his compilation of Martin Luther's '' Table Talk'', or notes taken of L ...
(1504–1565) in 1562 under the title "Sarepta oder Bergpostill".
[Ertl, 2006.] Up to about 1600, additional names used in the
German language
German ( ) is a West Germanic languages, West Germanic language mainly spoken in Central Europe. It is the most widely spoken and Official language, official or co-official language in Germany, Austria, Switzerland, Liechtenstein, and the Ita ...
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 the English words used for this mineral.
Dravite
![Black Dravite, Yinnietherra, Western Australia](https://upload.wikimedia.org/wikipedia/commons/2/2b/Black_Dravite%2C_Yinnietherra%2C_Western_Australia.jpg)
Dravite, also called brown tourmaline, is the sodium magnesium rich tourmaline endmember. Uvite, in comparison, is a calcium magnesium tourmaline. Dravite forms multiple series, with other tourmaline members, including schorl and elbaite.
The name ''dravite'' was used for the first time by
Gustav Tschermak (1836–1927), Professor of
Mineralogy
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...
and
Petrography
Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The classi ...
at the
University of Vienna
The University of Vienna (german: Universität Wien) is a public research university located in Vienna, Austria. It was founded by Duke Rudolph IV in 1365 and is the oldest university in the German-speaking world. With its long and rich histor ...
, in his book ''Lehrbuch der Mineralogie'' (published in 1884) for
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
-rich (and
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
-rich) tourmaline from village Dobrova near
Unterdrauburg in the
river area,
Carinthia
Carinthia (german: Kärnten ; sl, Koroška ) is the southernmost States of Austria, Austrian state, in the Eastern Alps, and is noted for its mountains and lakes. The main language is German language, German. Its regional dialects belong to t ...
,
Austro-Hungarian Empire
Austria-Hungary, often referred to as the Austro-Hungarian Empire,, the Dual Monarchy, or Austria, was a constitutional monarchy and great power in Central Europe between 1867 and 1918. It was formed with the Austro-Hungarian Compromise of ...
. Today this tourmaline locality (type locality for dravite) at Dobrova (near
Dravograd
Dravograd (; german: Unterdrauburg) is a small town in northern Slovenia, close to the border with Austria.
It is the seat of the Municipality of Dravograd. It lies on the Drava River at the confluence with the Meža and the Mislinja. It is ...
), is a part of the
Republic of Slovenia
Slovenia ( ; sl, Slovenija ), officially the Republic of Slovenia (Slovene: , abbr.: ''RS''), is a country in Central Europe. It is bordered by Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the southeast, and ...
.
[Ertl, 2007.] 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
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
: ''Drave'') in
Austria
Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
and Slovenia. The chemical composition which was given by Tschermak in 1884 for this dravite approximately corresponds to the formula , which is in good agreement (except for the
OH content) with the endmember formula of dravite as known today.
Dravite varieties include the deep green chromium dravite and the vanadium dravite.
Elbaite
![Elbaite-Lepidolite-Quartz-gem7-x1a](https://upload.wikimedia.org/wikipedia/commons/7/72/Elbaite-Lepidolite-Quartz-gem7-x1a.jpg)
A lithium-tourmaline
elbaite
Elbaite, a sodium, lithium, aluminium boro-silicate, with the chemical composition Na(Li1.5Al1.5)Al6Si6O18(BO3)3(OH)4, is a mineral species belonging to the six-member ring cyclosilicate tourmaline group.
Elbaite forms three series, with dravite, ...
was one of three pegmatitic minerals from
Utö,
Sweden
Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
, in which the new alkali element
lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
(Li) was determined in 1818 by
Johan August Arfwedson
Johan August Arfwedson (12 January 1792 – 28 October 1841) was a Swedish chemist who discovered the chemical element lithium in 1817 by isolating it as a salt.
Life and work
Arfwedson belonged to a wealthy bourgeois family, the son of th ...
for the first time.
[Ertl, 2008.] Elba Island
Elba ( it, isola d'Elba, ; la, Ilva) is a Mediterranean island in Tuscany, Italy, from the coastal town of Piombino on the Italian mainland, and the largest island of the Tuscan Archipelago. It is also part of the Arcipelago Toscano National ...
,
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
, was one of the first localities where colored and colorless Li-tourmalines were extensively chemically analysed. In 1850
Karl Friedrich August Rammelsberg Karl Friedrich August Rammelsberg (1 April 1813 – 28 December 1899) was a German mineralogist from Berlin, Prussia.
Life
After an apprenticeship in pharmacy, he studied chemistry and crystallography at the University of Berlin, where his influe ...
described
fluorine
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...
(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
Sušice (; german: Schüttenhofen) is a town in Klatovy District in the Plzeň Region of the Czech Republic. It has about 11,000 inhabitants. The historic town centre is well preserved and is protected by law as an urban monument zone.
Administr ...
,
Czech Republic
The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...
. In 1914
Vladimir Vernadsky
Vladimir Ivanovich Vernadsky (russian: link=no, Влади́мир Ива́нович Верна́дский) or Volodymyr Ivanovych Vernadsky ( uk, Володи́мир Іва́нович Верна́дський; – 6 January 1945) was ...
proposed the name ''Elbait'' for lithium-, sodium-, and aluminum-rich tourmaline from Elba Island, Italy, with the simplified formula .
Most likely the type material for elbaite was found at Fonte del Prete, San Piero in Campo,
Campo nell'Elba
Campo nell'Elba is a ''comune'' (municipality) on the island of Elba, in the Province of Livorno in the Italian region of Tuscany, located about southwest of Florence and about south of Livorno.
See also
*Monte Capanne
*Marina di Campo Airport
* ...
,
Elba
Elba ( it, isola d'Elba, ; la, Ilva) is a Mediterranean island in Tuscany, Italy, from the coastal town of Piombino on the Italian mainland, and the largest island of the Tuscan Archipelago. It is also part of the Arcipelago Toscano National ...
Island,
Province of Livorno
The province of Livorno or, traditionally, province of Leghorn ( it, provincia di Livorno) is a province in the Tuscany region of Italy. It includes several islands of the Tuscan Archipelago, including Elba and Capraia. Its capital is the city of ...
,
Tuscany
Tuscany ( ; it, Toscana ) is a Regions of Italy, region in central Italy with an area of about and a population of about 3.8 million inhabitants. The regional capital is Florence (''Firenze'').
Tuscany is known for its landscapes, history, art ...
,
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
.
In 1933 Winchell published an updated formula for elbaite, , which is commonly used to date written as .
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
San Diego County (), officially the County of San Diego, is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, making it California's second-most populous county and the fi ...
,
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
, United States.
Chemical composition
The tourmaline mineral group is chemically one of the most complicated groups of
silicate minerals
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
In mineralogy, silica (silicon dioxide, ) is usually con ...
. Its composition varies widely because of
isomorphous replacement Multiple isomorphous replacement (MIR) is historically the most common approach to solving the phase problem in X-ray crystallography studies of proteins. For protein crystals this method is conducted by soaking the crystal of a sample to be analyze ...
(solid solution), and its general formula can be written as , where:
* X =
Ca,
Na,
K,
▢ = vacancy
* Y =
Li,
Mg,
Fe2+,
Mn2+,
Zn,
Al,
Cr3+,
V3+,
Fe3+,
Ti4+,
▢ = vacancy
* Z = Mg, Al, Fe
3+, Cr
3+, V
3+
* T =
Si, Al,
B
* B = B,
▢ = vacancy
* V =
O H, O
* W = OH,
F, O
A revised nomenclature for the tourmaline group was published in 2011.
Physical properties
Crystal structure
![tourmaline01](https://upload.wikimedia.org/wikipedia/commons/6/64/Tourmaline01.jpg)
Tourmaline is a six-member ring
cyclosilicate
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
In mineralogy, silica (silicon dioxide, ) is usually consid ...
having a
trigonal
In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crysta ...
crystal system. It occurs as long, slender to thick prismatic and columnar
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s that are usually triangular in cross-section, often with curved striated faces. The style of termination at the ends of crystals is sometimes asymmetrical, called hemimorphism. Small slender prismatic crystals are common in a fine-grained
granite
Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...
called
aplite
Aplite () is an intrusive igneous rock in which the mineral composition is the same as granite, but in which the grains are much finer, under 1 mm across. Quartz and feldspar are the dominant minerals. The term ''aplite'' or ''aplitic'' ...
, 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
Euhedral crystals (also known as idiomorphic or automorphic crystals) are those that are well-formed, with sharp, easily recognised faces. The opposite is anhedral (also known as ''xenomorphic'' or ''allotriomorphic''): a rock with an anhedral ...
. 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
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied Stress (mechanics), mechanical s ...
, and are often
pyroelectric
Pyroelectricity (from the two Greek words ''pyr'' meaning fire, and electricity) is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the a ...
as well.
A crystal of tourmaline is built up of units consisting of a six-member silica ring that binds above to a large cation, such as sodium. The ring binds below to a layer of metal ions and hydroxyls or halogens, which structurally resembles a fragment of
kaolin
Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral ...
. This in turn binds to three triangular borate ions. Units joined end to end form columns running the length of the crystal. Each column binds with two other columns offset one-third and two-thirds of the vertical length of a single unit to form bundles of three columns. Bundles are packed together to form the final crystal structure. Because the neighboring columns are offset, the basic structural unit is not a
unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...
: The actual unit cell of this structure includes portions of several units belonging to adjacent columns.
File:Tourmaline oblique single.jpg, Oblique view of a single unit of the tourmaline crystal structure.
File:Tourmaline 001 single.png, View of single unit of tourmaline structure along the axis of the crystal
File:Tourmaline 100 3.png, View along a axis of three columns of tourmaline units forming a bundle
File:Tourmaline 001 mass.png, Structure of a tourmaline crystal viewed looking along the c axis of the crystal
Color
![Tourmaline Mineral Macro 2](https://upload.wikimedia.org/wikipedia/commons/c/c7/Tourmaline_Mineral_Macro_2.JPG)
Tourmaline has a variety of colors. Iron-rich tourmalines are usually 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
Watermelon (''Citrullus lanatus'') is a flowering plant species of the Cucurbitaceae family and the name of its edible fruit. A scrambling and trailing vine-like plant, it is a highly cultivated fruit worldwide, with more than 1,000 varieti ...
tourmaline and is prized in jewelry. An excellent example of watermelon tourmaline jewelry is a brooch piece (1969, gold, watermelon tourmaline, diamonds) by
Andrew Grima
Andrew Grima (31 May 1921 – 26 December 2007) was an Anglo-Italian designer who became known as the doyen of modern jewellery design in Britain.
Early life
Grima was born in Rome to Italian-Maltese parents and raised in London, where he atten ...
(British, b. Italy, 1921–2007), in the collection of Kimberly Klosterman and on display at the
Cincinnati Art Museum
The Cincinnati Art Museum is an art museum in the Eden Park neighborhood of Cincinnati, Ohio. Founded in 1881, it was the first purpose-built art museum west of the Alleghenies, and is one of the oldest in the United States. Its collection of ov ...
. Some forms of tourmaline are
dichroic
In optics, a dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths (colours) (not to be confused with dispersion), or one in which light rays having different polarizations are abs ...
; they change color when viewed from different directions.
The pink color of tourmalines from many localities is the result of prolonged natural irradiation. During their growth, these tourmaline crystals incorporated
Mn2+ and were initially very pale. Due to natural
gamma ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
exposure from
radioactive decay
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
of
40K in their
granitic
A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quart ...
environment, gradual formation of Mn
3+ ions occurs, which is responsible for the deepening of the pink to red color.
[Reinitz & Rossman, 1988.]
Magnetism
Opaque black schorl and yellow tsilaisite are idiochromatic tourmaline species that have high magnetic susceptibilities due to high concentrations of iron and manganese respectively. Most gem-quality tourmalines are of the elbaite species. Elbaite tourmalines are allochromatic, deriving most of their color and magnetic susceptibility from schorl (which imparts iron) and tsilaisite (which imparts manganese).
Red and pink tourmalines have the lowest magnetic susceptibilities among the elbaites, while tourmalines with bright yellow, green and blue colors are the most magnetic elbaites. Dravite species such as green chromium dravite and brown dravite are diamagnetic. A handheld
neodymium magnet
A hard_disk_drive.html"_;"title="Nickel-plated_neodymium_magnet_on_a_bracket_from_a_hard_disk_drive">Nickel-plated_neodymium_magnet_on_a_bracket_from_a_hard_disk_drive_
file:Nd-magnet.jpg.html" ;"title="hard_disk_drive_.html" ;"title="hard_disk_d ...
can be used to identify or separate some types of tourmaline gems from others. For example, blue indicolite tourmaline is the only blue gemstone of any kind that will show a drag response when a neodymium magnet is applied. Any blue tourmaline that is diamagnetic can be identified as paraiba tourmaline colored by copper in contrast to magnetic blue tourmaline colored by iron.
Treatments
Some tourmaline gems, especially pink to red colored stones, are altered by
heat treatment
Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also ...
to improve their color. Overly dark red stones can be lightened by careful heat treatment. The pink color in manganese-containing near-colorless to pale pink stones can be greatly increased by irradiation with gamma-rays or electron beams. Irradiation is almost impossible to detect in tourmalines, and does not, currently, affect the value. Heavily included tourmalines, such as rubellite and Brazilian paraiba, are sometimes clarity-enhanced. A clarity-enhanced tourmaline (especially the paraiba variety) is worth much less than an untreated gem of equal clarity.
Geology
Tourmaline is found in
granite
Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...
and granite
pegmatite
A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...
s and in
metamorphic
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...
rocks such as
schist
Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...
and
marble
Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or Dolomite (mineral), dolomite. Marble is typically not Foliation (geology), foliated (layered), although there are exceptions. In geology, the ...
. 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
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates) ...
and
conglomerate, and is part of the
ZTR index
The ZTR index is a method of determining how weathered,Prothero, D. R. and Schwab, F., 1996, Sedimentary Geology, pg. 460, both chemically and mechanically, a sediment (or a corresponding sedimentary rock) is. The letters in ZTR stand for 3 com ...
for highly weathered sediments.
Localities
Gem and specimen tourmaline is mined chiefly in
Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
and many parts of
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, including
Tanzania
Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...
,
Nigeria
Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg, Naijeriya officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf o ...
,
Kenya
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, ...
,
Madagascar
Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
,
Mozambique
Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi ...
,
Malawi
Malawi (; or aláwi Tumbuka: ''Malaŵi''), officially the Republic of Malawi, is a landlocked country in Southeastern Africa that was formerly known as Nyasaland. It is bordered by Zambia to the west, Tanzania to the north and northeast ...
, and
Namibia
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...
. It is also mined in
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
, notably in
Pakistan
Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...
,
Afghanistan
Afghanistan, officially the Islamic Emirate of Afghanistan,; prs, امارت اسلامی افغانستان is a landlocked country located at the crossroads of Central Asia and South Asia. Referred to as the Heart of Asia, it is bordere ...
, and
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
as well as in
Sri Lanka
Sri Lanka (, ; si, ශ්රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
and
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, where some placer material suitable for gem use is found.
United States
Some fine gems and specimen material have been produced in the United States, with the first discoveries in 1822, in the state of
Maine
Maine () is a state in the New England and Northeastern regions of the United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Canadian provinces of New Brunswick and Quebec to the northeast and north ...
. 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 Cixi
Empress Dowager Cixi ( ; mnc, Tsysi taiheo; formerly Romanization of Chinese, romanised as Empress Dowager T'zu-hsi; 29 November 1835 – 15 November 1908), of the Manchu people, Manchu Nara (clan)#Yehe Nara, Yehe Nara clan, was a Chinese nob ...
of China loved pink tourmaline and bought large quantities for gemstones and carvings from the then new Himalaya Mine, located in
San Diego County
San Diego County (), officially the County of San Diego, is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, making it California's second-most populous county and the fi ...
, California. 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, California
Pala is a small, mostly Native American, community and CDP located in the Pala Indian Reservation, located within San Diego County, California. For centuries a traditional gathering place of native peoples, it was selected in the early 19th ce ...
in
San Diego County
San Diego County (), officially the County of San Diego, is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, making it California's second-most populous county and the fi ...
.
Brazil
Almost every color of tourmaline can be found in Brazil, especially in the Brazilian states of
Minas Gerais
Minas Gerais () is a state in Southeastern Brazil. It ranks as the second most populous, the third by gross domestic product (GDP), and the fourth largest by area in the country. The state's capital and largest city, Belo Horizonte (literally ...
and
Bahia
Bahia ( , , ; meaning "bay") is one of the 26 Federative units of Brazil, states of Brazil, located in the Northeast Region, Brazil, Northeast Region of the country. It is the fourth-largest Brazilian state by population (after São Paulo (sta ...
. The new type of tourmaline, which soon became known as paraiba tourmaline, came in blue and green. Brazilian paraiba tourmaline usually contains abundant inclusions. Much of the paraiba tourmaline from Brazil actually comes from the neighboring state of
Rio Grande do Norte
Rio Grande do Norte (, , ) is one of the states of Brazil. It is located in the northeastern region of the country, forming the northeasternmost tip of the South American continent. The name literally translates as "Great Northern River", ref ...
. 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.
[Rossman et al. 1991.]
A large bluish-green tourmaline from Paraiba, measuring and weighing , is the world's largest cut tourmaline.
Owned by Billionaire Business Enterprises,
it was presented in
Montreal
Montreal ( ; officially Montréal, ) is the List of the largest municipalities in Canada by population, second-most populous city in Canada and List of towns in Quebec, most populous city in the Provinces and territories of Canada, Canadian ...
,
Quebec
Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee ...
,
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
, on 14 October 2009.
Africa
![Paraiba-Turmalin-Mosambik-G-EmpireTheWorldOfGems](https://upload.wikimedia.org/wikipedia/commons/6/68/Paraiba-Turmalin-Mosambik-G-EmpireTheWorldOfGems.jpg)
In the late 1990s, copper-containing tourmaline was found in
Nigeria
Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg, Naijeriya officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf o ...
. 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
Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi ...
has also produced 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.
Another highly valuable variety is chrome tourmaline, a rare type of dravite tourmaline from
Tanzania
Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...
. Chrome tourmaline is a rich green color due to the presence of chromium atoms in the crystal. Of the standard elbaite colors, blue indicolite gems are typically the most valuable,
followed by green verdelite and pink to red rubellite.
See also
*
Benjamin Wilson – experimented with the electrical properties of tourmaline
References
Citations
General and cited sources
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Further reading
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External links
Tourmaline classificationICA's tourmaline pageInternational Colored Gemstone Association on Tourmaline
Farlang historical tourmaline referencesUS localities, antique references
Webmineral elbaite page crystallographic and mineral information on elbaite
Tourmaline History and Loreat GIA.edu
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Aluminium minerals
Cyclosilicates
Gemstones
Iron minerals
Lithium minerals
Manganese minerals
Minerals in space group 160
Sodium minerals
Trigonal minerals