Tourmaline: description, properties and photo
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.
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.
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.