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Encyclopedia > Tourmaline
Tourmaline

Schorl Tourmaline
General
Category mineral group
Chemical formula (Ca,K,Na,[])(Al,Fe,Li,Mg,Mn)3(Al,Cr, Fe,V)6
(BO3)3(Si,Al,B)6O18(OH,F)4
[1][2]
Identification
Color Most commonly black, but can range from brown, violet, green, pink, or in a dual-colored pink and green.
Crystal habit Parallel and elongated. Acicular prisms, sometimes radiating. Massive. Scattered grains (in granite).
Crystal system Trigonal
Cleavage Indistinct
Fracture Uneven, small conchoidal, brittle
Mohs Scale hardness 7 - 7.5
Luster Vitreous, sometimes resinous
Polish luster Vitreous[1]
Refractive index nω=1.635 - 1.675, nε=1.610 - 1.650
Optical Properties Double refractive, uniaxial negative[1]
Birefringence -0.018 to -0.040; typically about .020 but in dark stones it may reach .040[1]
Dispersion .017[1]
Pleochroism typically moderate to strong[1]
Red Tourmaline: Definite; dark red,light red
Green Tourmaline: Strong; dark green, yellow-green
Brown Tourmaline: Definite; dark brown, light brown
Blue Tourmaline: Strong; dark blue, light blue
Ultraviolet fluorescence pink stones - inert to very weak red to violet in long and short wave[1]
Absorption spectra a strong narrow band at 498nm, and almost complete absorption of red down to 640nm in blue and green stones; red and pink stones show lines at 458 and 451nm as well as a broad band in the green spectrum[1]
Streak White
Specific gravity 3.06 (+.20 -.06)[1]
Density 2.82 - 3.32

The tourmaline mineral group is chemically one of the most complicated groups of silicate minerals. It is a complex silicate of aluminium and boron, but because of isomorphous replacement (solid solution), its composition varies widely with sodium, calcium, iron, magnesium, lithium and other elements entering into the structure. Tourmaline. ... This article or section does not cite any references or sources. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... A crystal system is a category of space groups, which characterize symmetry of structures in three dimensions with translational symmetry in three directions, having a discrete class of point groups. ... In crystallography, the rhombohedral (or trigonal) crystal system is one of the 7 lattice point groups. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... For fractures in geologic formations, see Rock fracture. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Dispersion of a light beam in a prism. ... Pleochroism is an optical phenomenon in which grains of a rock appear to be different colors when observed at different angles,under a petrographic microscope. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... Absorption spectroscopy refers to a wide range of techniques where one measures how much light of a particular wavelength (color) is absorbed by a sample. ... The streak (also called powder color) of a mineral is the color of the powder produced when it is dragged across a unweathered surface. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. ... The silicate minerals make up the largest and most important class of rock-forming minerals. ... In chemistry, a silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Standard atomic weight 26. ... General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black/brown Standard atomic weight 10. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Standard atomic weight 22. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/grey Standard atomic weight 6. ...


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. Interestingly, 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. In crystallography, the rhombohedral (or trigonal) crystal system is one of the 7 lattice point groups. ... Quartz crystal Synthetic bismuth hopper crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid in which the constituent atoms... Quartz crystal Synthetic bismuth hopper crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid in which the constituent atoms... Close-up of granite from Yosemite National Park, valley of the Merced River Quarrying granite for the Mormon Temple, Utah Territory. ... Aplite is a fine to very fine-grained sugary-textured rock of granite composition. ... Euhedral refers to well formed crystals with sharp easily recognised faces. ... The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ...


All hemimorphic crystals are piezoelectric, and are often pyroelectric as well. Tourmaline crystals when warmed become positively charged at one end and negatively charged at the other. Due to this effect, tourmaline crystals in collections may attract unsightly coatings of dust when displayed under hot spotlights. Tourmaline's unusual electrical properties made it famous in the early 18th century. 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. Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress. ... Pyroelectricity is the ability of certain materials to generate an electrical potential when they are heated or cooled. ... This article needs additional references or sources to facilitate its verification. ...


Tourmaline has a wide 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 practically any color: blue, green, red, yellow, pink etc. Rarely, it is colorless. Bi-colored and multicolored crystals are relatively common, reflecting variations of fluid chemistry during crystallisation. 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 appear to change color when viewed from different directions. Color is an important part of the visual arts. ... The brown and orange disks of color are objectively identical, in identical gray surrounds, in this image; their perceived color categories depend on what white they are compared to. ... A yellow Tulip. ... Binomial name (Thunb. ... In optics, the term dichroic has two related but distinct meanings. ...


The most common variety 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 the year 1400 (AD) 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, a lot of black tourmaline was found. The first relatively detailed 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" (Ertl, 2006). Up to about 1600, additional names used in the German language were "Schurel", "Schörle", and "Schurl". From the 18th century on, the name "Schörl" was mainly used in the German-speaking area. In English, the names "shorl" and "shirl" were used in the 18th century for schorl. In the 19th century the names "common schorl", "schörl", "schorl" and "iron tourmaline" were used in the Anglo-Saxon area (Ertl, 2006). The word tourmaline has two entymologies, both from the Sinhalese word turamali, meaning "stone attracting ash" (a reference to its pyroelectric properties) or according to other sources "mixed gemstones". The meaning of the word "schorl" is a mystery, but it may be a Scandinavian word. Events Henry IV quells baron rebellion and executes The Earls of Kent, Huntingdon and Salisbury for their attempt to have Richard II of England restored as King Jean Froissart writes the Chronicles Medici family becomes powerful in Florence, Italy Births December 25 - John Sutton, 1st Baron Dudley, Lord Lieutenant of... Zschorlau is a municipality in the district of Aue-Schwarzenberg, in Saxony, Germany. ... Location Time zone CET/CEST (UTC+1/+2) Administration Country NUTS Region DED Capital Dresden Minister-President Georg Milbradt (CDU) Governing parties CDU / SPD Votes in Bundesrat 4 (from 69) Basic statistics Area  18,416 km² (7,110 sq mi) Population 4,252,000 (11/2006)[1]  - Density 231 /km... Cassiterite is a tin oxide mineral, SnO2. ... Johannes Mathesius (1504–1565) Johannes Mathesius (1504-06-24 – 1565-10-07), also called Johann Mathesius or John Mathesius, was a German minister and a Lutheran reformer. ... 1504 was a leap year starting on Friday (see link for calendar) of the Gregorian calendar. ... // Events March 1 - the city of Rio de Janeiro is founded. ... Year 1562 was a common year starting on Thursday (link will display the full calendar) of the Julian calendar. ... 1600 was a leap year starting on Saturday of the Gregorian calendar (or a leap year starting on Tuesday of the 10-day slower Julian calendar). ... German (called Deutsch in German; in German the term germanisch is equivalent to English Germanic), is a member of the western group of Germanic languages and is one of the worlds major languages. ... The English language is a West Germanic language that originates in England. ... Year 2006 (MMVI) was a common year starting on Sunday (link displays full 2006 calendar) of the Gregorian calendar. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Scandinavia is a historical and geographical region centered on the Scandinavian Peninsula in Northern Europe and includes the three kingdoms of Denmark, Norway and Sweden. ...


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 Mg-rich (and Na-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 (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: 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 (Ertl, 2007).


Tourmaline is found in two main geological occurrences. Igneous rocks, in particular granite and granite pegmatite 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. Also, tourmaline is a durable mineral and can be found in minor amounts as grains in sandstone and conglomerate. Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Close-up of granite from Yosemite National Park, valley of the Merced River Quarrying granite for the Mormon Temple, Utah Territory. ... This article or section does not cite its references or sources. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ... Venus de Milo, front. ... Close-up of granite from Yosemite National Park, valley of the Merced River Quarrying granite for the Mormon Temple, Utah Territory. ... This article or section does not cite its references or sources. ... Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ... Venus de Milo, front. ... Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth due to erosion by flash flooding over millions of years Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. ... A conglomerate with iron oxide cementing material Conglomerate, Submarine Landslide located at Point Reyes, Marin County California. ...

Bi-colored tourmaline crystal, 0.8 inches long (2 cm).
Bi-colored tourmaline crystal, 0.8 inches long (2 cm).

Today, gem and specimen tourmaline is mined chiefly in Brazil and Africa. Some placer material suitable for gem use comes from Sri Lanka. Some fine gem and specimen material has been produced in the US, with the first discoveries having been made 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 interesting bicolors. During the early 1900s, Maine and California were the worlds largest producers of gem tourmalines. The Empress Dowager Tz'u Hsi, the last Empress 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. [3] Download high resolution version (750x1039, 73 KB)Bi-coloured tourmaline crystal, 0. ... Download high resolution version (750x1039, 73 KB)Bi-coloured tourmaline crystal, 0. ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... Official language(s) None (English and French de facto) Capital Augusta Largest city Portland Area  Ranked 39th  - Total 33,414 sq mi (86,542 km²)  - Width 210 miles (338 km)  - Length 320 miles (515 km)  - % water 13. ... Official language(s) English Capital Sacramento Largest city Los Angeles Area  Ranked 3rd  - Total 158,302 sq mi (410,000 km²)  - Width 250 miles (400 km)  - Length 770 miles (1,240 km)  - % water 4. ... Empress Dowager Cixi (Chinese: ; pinyin: ; Wade-Giles: Tzu-Hsi Tai-hou) (November 29, 1835 – November 15, 1908), popularly known in China as the West Empress Dowager (Chinese: 西太后), was from the Manchu Yehe Nara Clan. ... San Diego County is a county located on the Pacific Ocean in the far southwest of California, along the border with Mexico. ...


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. The demand and excitement for this new material, which has fetched more than $50,000 per carat, earned more respect for the other colors of tourmaline. In the late 90s, 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. Flag of Minas Gerais See other Brazilian States Capital Belo Horizonte Largest City Belo Horizonte Area 586,528. ... Flag of Bahia See other Brazilian States Capital Salvador Largest City Salvador Area 564 273 km² Population   - Total   - Density 13 070 250 23. ... Year 1989 (MCMLXXXIX) was a common year starting on Sunday (link displays 1989 Gregorian calendar). ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic pinkish red Standard atomic weight 63. ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... Paraíba is one of the states of Brazil, located in the northeastern part of the country, on the Atlantic coast. ...


Another unique variety that is also highly valued is chrome tourmaline, a rare type of dravite tourmaline from Tanzania which occurs in a very rich green color caused by chromium, the same element which causes the green in emerald. Of the standard Elbaite colors, generally blue indicolite gems are the most expensive, followed by green verdelite and pink to red rubellite. There are also yellow tourmalines, sometimes known as canary tourmaline. Ironically the rarest variety, colorless achroite, is not appreciated and is the least expensive of the transparent tourmalines. In addition to Brazil, significant amounts of tourmaline are also mined in Tanzania, Nigeria, Kenya, Madagascar, Mozambique, Namibia, Afghanistan, Pakistan, and Sri Lanka, and Malawi.[4]


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, which must be disclosed to the buyer. A clarity-enhanced tourmaline (especially paraiba) is worth much less than a non-treated gem.[5] Irradiation is the process by which an item is exposed to radiation. ...


Tourmaline Species and Varieties

Large Pink Elbaite Crystal on Quartz, Cryo-Genie Mine, San Diego Co., California, USA
Large Pink Elbaite Crystal on Quartz, Cryo-Genie Mine, San Diego Co., California, USA
  • 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
    • Rose or pink - rubellite variety(from ruby)
    • Dark blue - indicolite variety (from indigo)
    • Light blue - Brazilian sapphire variety
    • Green - verdelite or Brazilian emerald variety
    • Colorless - achroite variety (from the Greek for "colorless")
Tri-color Elbaite Crystals on Quartz, Himalaya Mine, San Diego Co., California, USA
The 14 recognized minerals in the group (endmember formulas)
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

Image File history File links Size of this preview: 488 × 599 pixel Image in higher resolution (600 × 737 pixel, file size: 130 KB, MIME type: image/jpeg) Source: Chris Ralph. ... Image File history File links Size of this preview: 488 × 599 pixel Image in higher resolution (600 × 737 pixel, file size: 130 KB, MIME type: image/jpeg) Source: Chris Ralph. ... Carinthia (German: Kärnten, Slovenian: Koroška) is the southernmost Austrian state or Land; it is chiefly famous for its mountains and lakes. ... Elba (bottom centre) from space, February 1994. ... Ruby is a red gemstone. ... Indigo is the color on the spectrum between about 450 and 420 nm in wavelength, placing it between blue and violet. ... Sapphire (from Hebrew: ספיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... This article or section does not cite its references or sources. ... Image File history File links Size of this preview: 459 × 599 pixel Image in higher resolution (1000 × 1306 pixel, file size: 227 KB, MIME type: image/jpeg) Source: Chris Ralph. ... Image File history File links Size of this preview: 459 × 599 pixel Image in higher resolution (1000 × 1306 pixel, file size: 227 KB, MIME type: image/jpeg) Source: Chris Ralph. ... Buergerite is a mineral species belonging to the tourmaline group. ... Elbaite is gemstone, reckoned to be one of the most desirable of the Tourmaline family because of the vaiety and depth of its colours and quality of the crystals. ... The mineral tourmaline is chemically one of the most complicated silicate minerals. ...

Notes

  1. ^ a b c d e f g h i Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  2. ^ Mindat tourmaline group Accessed September 12, 2005. This website details specifically and clearly how the complicated chemical formula is structured.
  3. ^ Exploring and Mining Gems and Gold in the West, By Fred Rynerson - Naturegraph Publishers.
  4. ^ Manual of Mineralogy (after Dana), 19th Edition, By Hurlbut and Klien - John Wiley and Sons, Publishers
  5. ^ Gemstone Enhancement: Heat, Irradiation, Impregnation, Dyeing, and Other Treatments by Kurt Nassau; Butterworth Publishers 1984

The Gemological Institute of America, or GIA, is a non-profit institute dedicated to research and education in the field of gemology. ... is the 255th day of the year (256th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ...

References

Wikimedia Commons has media related to:
Tourmaline
  • Tourmaline classification Accessed September 12, 2005
  • Mindat tourmaline group Accessed September 12, 2005
  • Mineral galleries Accessed September 12, 2005
  • Gemstone.org
  • AGTA.organd addmorecolortoyourlife.com American Gem Trade Association pages on Tourmaline
  • Ertl, A., Pertlik, F. & Bernhardt, H.-J. (1997) Investigations on olenite with excess boron from the Koralpe, Styria, Austria, Österreichische Akademie der Wissenschaften, Mathematisch-Naturwissenschaftliche Klasse, Abt. I, Anzeiger, 134, pp 3-10. [1]
  • Ertl, A. (2006) About the etymology and the type localities of schorl Mitteilungen der Österreichischen Mineralogischen Gesellschaft, 152, 2006, pp 7–16. [2]
  • Ertl, A. (2007) About the type locality and the nomenclature of dravite Mitteilungen der Österreichischen Mineralogischen Gesellschaft, 153, 2007, pp 265–271. [3]
  • Schumann, Walter (2006) Gemstones of the World 3rd Edition Sterling Publishing, New York; pp 126-127

  Results from FactBites:
 
Tourmaline - Wikipedia, the free encyclopedia (600 words)
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.
Usually, iron-rich tourmalines are fl to bluish-fl to deep brown, while magnesium-rich varieties are brown to yellow, and lithium-rich tourmalines are practically any color: blue, green, red, yellow, pink etc. Rarely, it is colourless.
Magnesium-rich tourmalines, dravites, are generally restricted to schists and marble.
Maine's State Mineral - Maine Geological Survey (922 words)
Tourmaline is one of the most attractive minerals occurring in Maine.
Tourmaline is actually a group of several different minerals which have similar crystal structures, but complex and variable chemical formulas.
Tourmaline crystals and gems from Maine, including the Peary Necklace and one of the largest crystals from Newry, are on display at the Maine State Museum in Augusta.
  More results at FactBites »

 
 

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