Tourmaline gemstone

Tourmaline gemstone


Published On: 07-02-2012 11:34pm

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Category: Gemstones

Tourmaline Blog

My latest gemstone love is Tourmaline.  This gem has such a great range of colors with an earthy feel.

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.


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.

Tourmaline has a variety of colors. Usually, iron-rich tourmaline 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. The pink color of tourmaline from many fields is the result of a continued natural irradiation.


Some tourmaline gems, especially pink to red colored stones, are altered by irradiation to improve their color. Irradiation is almost impossible to detect in tourmaline, and does not impact the value. Heavily-included tourmaline, 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.

The name tourmaline comes from the Singhalese words 'tura mali'. In translation, this means something like 'stone with mixed colors’, referring to the color spectrum of this gemstone, which outdoes that of all other precious stones. There are tourmaline from red to green and from blue to yellow. They often have two or more colors. There are tourmaline which change their color when the light changes from daylight to artificial light, and some show the light effect of a cat's eye. No two tourmaline are exactly alike. This gemstone has an endless number of faces, and for that reason it suits all moods. This gemstone has excellent wearing qualities and is easy to look after, for all tourmaline have a good hardness of 7 to 7.5 on the Mohs scale. So the tourmaline is an interesting gemstone in many ways. 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. 

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. 


In the trade, the individual color 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 color changes when the light source does, the stone is called a pink or shocking pink tourmaline. In the language of the gemologists, blue tourmaline 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 tourmaline 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 tourmaline from Malawi with a vivid yellow color, known as 'canary tourmaline', came into the trade, the color yellow, which was previously very scarce indeed, has been very well represented in the endless spectrum of colors boasted by the 'gemstone of the rainbow'.

Yet the tourmaline has even more names: stones with two colors are known as bi colored tourmaline, and those with more than two as multicolored tourmaline. 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 color variety of this gemstone. If the center of the slice is red and the area around it green, the stone is given the nickname 'watermelon'.

 

Sources:

 http://en.wikipedia.org/wiki/Tourmaline

http://www.gemstone.org/index.php?option=com_content&view=article&id=110:sapphire&catid=1:gem-by-gem&Itemid=14

http://www.minerals.net/gemstone/tourmaline.aspx


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