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Tourmaline: description, properties and photo

Tourmaline

Tourmaline is a gemstone with amazing properties. This gemstone in its diversity of colors surpasses any other gem. The stone got its name in Europe at the beginning of the 18th century, when Dutch sailors began to bring various gems from Ceylon island (Sri Lanka) and among them – golden columnar crystals, which the inhabitants of the island called “turamali” or “turmali”. Mineral crystals are often represented by prisms with longitudinal shading. The cross section of the crystals usually looks like a spherical triangle. The hardness is quite high (7-7.5), it can be safely used in jewelry. Tourmalines today include a whole group of minerals with a common crystalline structure, but with differences in chemical composition.

Tourmaline

There are two different classifications of tourmaline group minerals: crystallochemical — the name of the stone was derived from its chemical composition and crystal structure; and color classification, often used in gemology and commerce.
According to the crystal chemical classification in mineralogy there are few main varieties, which distinguished that can be used in jewelry:

  • Elbaite. Color description: pink, red, green, blue, yellow, colorless, polychrome.
  • Liddicoatite. Color description: pink, green, blue, yellow, brown, colorless, often polychrome.
  • Dravit. Color description: brown to black, red, yellow, blue, green, colorless.
  • Chromdaravite. Color description: dark green to black.
  • Uvit. Color description: brown to black, from light to dark green, red.
  • Schorl. Color description: black, dark brown, blue-black. Interestingly, that in very thin transparent sections, the stone has a blue, green, red or yellow color.

Most tourmalines of gem quality are elbaites in their composition.

In the color classification, the following names of the varieties of the mineral were established: rubellite – pink to red,  verdelite – green,  indiсolite  – blue,  achroite – colorless (white). Samples of intense green color, stained with chromium, can be called chrometourmaline. Paraiba, first found in the 1980s in Brazil, in the state of Paraiba, is considered the most expensive type of mineral. This stone, containing copper, has its characteristic bright “neon” blue, green and blue-violet colors. In its composition, it is usually considered to be elbaite.
When describing varieties of a mineral, they are often limited only by indicating their color without using any other names, for example, pink tourmaline, green tourmaline etc.

In addition to the specimens painted in the same color as mentioned above, there are polychrome tourmalines or multicolor ones. It is characteristic of this species that two, three, and even more colors can be observed in the same crystal with the naked eye. For example, color zones can be located across the main axis of the crystal, or form concentric layers in transverse sections of the crystal. If the central zone in the cross section of the tourmaline crystal is pink or red, and the outer border is green, then it will be called “watermelon”.

Neon blue Paraiba, pink-red rubellites and blue indigolites are the most valuable varieties of tourmaline.

DEPOSITS

The main part of gem tourmalines with different colors is supplied to the world market from Brazil. More than half of all tourmalines are mined there. Most deposits are located in the state of Minas Gerais. From African countries that extract the mineral, Mozambique, Nigeria and Madagascar can be distinguished. Anjanabonoina deposit in Madagascar produces the richest by color polychrom liddicoatites. Expensive copper-containing Paraiba is now mined mainly in Mozambique. Brazilian deposits of this gem in the Paraiba and Rio Grande do Norte states are practically depleted. A small amount of Paraiba crystals used to come from Nigeria and Kongo. Tourmaline also mined in Afghanistan, Pakistan and Tajikistan. Also it comes from Europe, where it is mined in Italy on the island of Elba. In the USA, deposits are also available, especially the collection specimens of rubellite from California. In Russia, tourmaline is mainly mined at the Malkhan deposit in Transbaikalia. The first finds in the Urals in Russia were made at the end of the 18th century. But now Ural crystals are more likely to be of collector interest only because of their rarity.

Tourmaline Crysral

Properties

Mineral:

tourmaline

Chemical formula:

XY3Al6 (OHF) 4 [BO3] 3 [Si6O18], where X = Na, Ca, Li, and Y = Fe2 +, Mg, Mn, Al, G, V

Crystal Systems:

trigonal

Mohs scale hardness:

7-7.5

Optical character:

Anisotropic

Cleavage:

none

Density:

3.06 (+0.20, -0.06) g / cm3

Luster:

Vitreous

Refractive index:

1,624-1,644

Birefringence:

0.018-0.040

Dispersion:

0.017

Color:

all colors

Interesting facts

  • In cross sections of liddicoatites crystals from Madagascar more than five different colors can be observed in same samples.
  • Light pink tourmalines are still called rubellites in Russia, but abroad they are “pink”, and only samples of saturated pink-red or red color will be called rubellites.
  • Tourmalines have an interesting property: they are electrified under the influence of heating and cooling, under tension and compression, and also under the influence of friction.
Tourmaline Crysral

History

The first tourmalines were brought to Europe by Dutch sailors from Ceylon island (Sri Lanka) in 1703. Sailors cleaned their smoking pipes from the ashes with long tourmaline crystals. This was facilitated by amazing properties: tourmalines are electrified by heating and can attract ashes. Due to the variety of colors, they were often mistaken for other colored stones. For example, it turned out that in the crown of Czech kings there is not a ruby, but a red rubellite. The crown of the Russian Empress Anna Ioannovna was also decorated with a pink tourmaline stone, and not spinel, as previously thought. The Diamond Fund of Russia contains the “Big Ruby”, donated in 1777 to Empress Catherine II by the Swedish king Gustav III, it is also a tourmaline. Rubellites from the mid-18th century became very popular in Europe and Russia. The jeweler Pierre-Karl Fabergé, who actively used them in his jewelry and decor items, also contributed to the increase in popularity. A large flow of gem to the world market was associated with the discovery of huge deposits in Brazil. In 1989, a sensation occurred at an exhibition in Tucson (USA): an unprecedented gem was presented to the public - a neon blue Paraiba tourmaline. The color diversity of tourmalines was appreciated by many famous jewelry companies, and the cost of these stones is growing very quickly.

Enhancement

Gemstones can sometimes be subjected to various treatment methods to improve their beauty. Heat treatment can be used to lighten too dark green and blue-green tourmaline. Pink-red samples can completely discolor by heating. Only very dark samples are subjected to short-term low-temperature heat treatment in order to clarify. Unwanted pink-violet shades in Paraiba copper-containing tourmalines are also removed under the temperature influence, revealing their blue and greenish-blue color. Irradiation can be used to improve the color saturation of pink/red samples. Colorless stones can become pink after irradiation, and light yellow stones may become brighter or also turn pink/red. Cracks can be filled with various polymers to visually improve the clarity of the tourmaline. Such filling can be subjected, for example, to heat-treated Paraiba, which are characterized by many cracks. To bleach the channels in tourmalines, etching with various acids is rarely used. Udentification of treatment is important primarily for the expensive Paraiba tourmaline variety, as the price of a stone can strongly depend on the facts of heat treatment and filling.

Tourmaline

Photo

a watermelon tourmaline crystal variety from Nigeria

Cross section of a watermelon tourmaline crystal variety from Nigeria

tourmaline of different facets and colors

On the photo: tourmaline of different facets and colors

Paraiba blue tourmaline (Mozambique)

In the photo the most expensive kind of tourmaline mineral: 13.65 carat Paraiba blue tourmaline (Mozambique)

red rubellite in cushion shape

On the photo: a large sample of a red rubellite in cushion shape

Vivid color rubellite in trillion shape

Vivid color rubellite in trillion shape

Faceted green verdelite Brazil

Faceted green verdelite 26.13 carats from Cruzeiro Mine, Brazil

green tourmaline (Afghanistan)

On the photo: a 38.49-carat green tourmaline (Afghanistan)

Large Paraiba tourmalines from Mozambique

Large Paraiba tourmalines from Mozambique

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