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Tourmaline/碧玺
Macumbahttp://baike.baidu.com/view/3391408.htm
Tourmalines are gems with an incomparable variety of colours. The
reason, according to an old Egyptian legend, is that the tourmaline, on its
long journey up from the centre of the Earth, passed over a rainbow. In doing
so, it assumed all the colours of the rainbow. And that is why it is still
referred to as the 'gemstone of the rainbow' today.
The name tourmaline comes from the Singhalese words 'tura mali'. In
translation, this means something like 'stone with mixed colours', referring to
the colour spectrum of this gemstone, which outdoes that of all other precious
stones. There are tourmalines from red to green and from blue to yellow. They
often have two or more colours. There are tourmalines which change their colour
when the light changes from daylight to artificial light, and some show the
light effect of a cat's eye. No two tourmalines are exactly alike. This
gemstone has an endless number of faces, and for that reason it suits all
moods. 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.
Colours, names and nicknames
In order to understand this variety of colour, you will have to
brush up your knowledge of gemmology a little: tourmalines are mixed crystals
of aluminium boron silicate with a complex and changing composition. The
mineral group is a fairly complex one. Even slight changes in the composition
cause completely different colours. Crystals
of only a single colour are fairly rare; indeed the same crystal will often
display various colours and various nuances of those colours. And the trademark
of this gemstone is not only its great wealth of colour, but also its marked
dichroism. Depending on the angle from which you look at it, the colour may be
different or more or less intense. It is always at its most intense when viewed
looking toward the main axis, a fact to which the cutter must pay great
attention when lining up the cut. This gemstone has excellent wearing qualities
and is easy to look after, for all tourmalines have a good hardness of 7 to 7.5
on the Mohs scale. So the tourmaline is an interesting gemstone in many ways.
TIn the trade, the individual colour 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 colour
changes when the light source does, the stone is called a pink or shocking pink
tourmaline.  In
the language of the gemmologists, blue tourmalines 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
tourmalines 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 tourmalines from Malawi with a
vivid yellow colour, known as 'canary tourmalines', came into the trade, the
colour yellow, which was previously very scarce indeed, has been very well
represented in the endless spectrum of colours boasted by the 'gemstone of the
rainbow'.
Yet the tourmaline has even more names: stones with two colours
are known as bicoloured tourmalines, and those with more than two as multicoloured
tourmalines. 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 colour variety of this gemstone. If the centre of the slice is red
and the area around it green, the stone is given the nickname 'water melon'.  On the other hand, if the crystal is
almost colourless and black at the ends only, it is called a 'Mohrenkopf', (resembling a certain kind of cake popular in
Germany).
Tourmalines are found almost all over the world. There are major
deposits in Brazil, Sri Lanka and
South and south-west Africa. Other finds have been made in Nigeria, Zimbabwe,
Kenya, Tanzania, Mozambique,
Madagascar, Pakistan and Afghanistan. Tourmalines are also
found in the USA, mainly in California and Maine.
Although there are plenty of gemstone deposits which contain tourmalines, good
qualities and fine colours are not often discovered among them. For this
reason, the price spectrum of the tourmaline is almost as broad as that of its
colour.
The 'aschentrekker'
It is not only designers who love the tourmaline on account of its
inspiring variety of colour. Scientists too are interested in it because of its
astonishing physical qualities, for tourmalines can become electrically charged
when they are heated and then allowed to cool. Then, they have a positive
charge at one end and a negative one at the other. This is known as
'pyro-electricity', derived from the Greek word 'pyr', meaning fire. The
gemstone also becomes charged under pressure, the polarity subsequently
changing when the pressure is taken off. When the charge changes, the
tourmaline begins to oscillate, similar to a rock crystal but much more
pronouncedly. The Dutch, who were the first to bring the tourmaline to Europe, were familiar with this effect a long time before
it was able to be provided with a scientific explanation. They used a heated
tourmaline to draw up the ash from their meerschaum pipes, and called the
gemstone with the amazing powers an 'aschentrekker'.
In the fascinating world of gemstones, the tourmaline is very
special. Its high availability and its glorious, incomparable colour spectrum
make it one of our most popular gemstones - and apart from that, almost every
tourmaline is unique.
原文出处：http://www./index.php?option=com_content&view=article&id=110:sapphire&catid=1:gem-by-gem&Itemid=14
中文介绍: http://baike.baidu.com/view/10387.htm#6
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