新出生婴儿脸上起红点:碧玺英文介绍

Tourmaline/碧玺

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Tourmalines are gems with an incomparable variety of colours. Thereason, according to an old Egyptian legend, is that the tourmaline, on itslong journey up from the centre of the Earth, passed over a rainbow. In doingso, it assumed all the colours of the rainbow. And that is why it is stillreferred to as the 'gemstone of the rainbow' today.

The name tourmaline comes from the Singhalese words 'tura mali'. Intranslation, this means something like 'stone with mixed colours', referring tothe colour spectrum of this gemstone, which outdoes that of all other preciousstones. There are tourmalines from red to green and from blue to yellow. Theyoften have two or more colours. There are tourmalines which change their colourwhen the light changes from daylight to artificial light, and some show thelight effect of a cat's eye. No two tourmalines are exactly alike. Thisgemstone has an endless number of faces, and for that reason it suits allmoods. No wonder that magical powers have been attributed to it since ancienttimes. In particular, it is the gemstone of love and of friendship, and is saidto render them firm and long-lasting.

Colours, names and nicknames

In order to understand this variety of colour, you will have tobrush up your knowledge of gemmology a little: tourmalines are mixed crystalsof aluminium boron silicate with a complex and changing composition. Themineral group is a fairly complex one. Even slight changes in the compositioncause completely different colours. Crystalsof only a single colour are fairly rare; indeed the same crystal will oftendisplay various colours and various nuances of those colours. And the trademarkof this gemstone is not only its great wealth of colour, but also its markeddichroism. Depending on the angle from which you look at it, the colour may bedifferent or more or less intense. It is always at its most intense when viewedlooking toward the main axis, a fact to which the cutter must pay greatattention when lining up the cut. This gemstone has excellent wearing qualitiesand is easy to look after, for all tourmalines have a good hardness of 7 to 7.5on the Mohs scale. So the tourmaline is an interesting gemstone in many ways.

TIn the trade, the individual colour variants have their ownnames. For example, a tourmaline of an intense red is known as a 'rubellite', but only if it continues to display thesame fine ruby red in artificial light as it did in daylight. If the colourchanges when the light source does, the stone is called a pink or shocking pinktourmaline.  Inthe 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 tohave 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, itis referred to as a 'chrome tourmaline'. The absolute highlight among thetourmalines is the 'Paraiba tourmaline', a gemstone of an intense blue toblue-green which was not discovered until 1987 in a mine in the Brazilian stateof Paraiba. In good qualities, these gemstonesare much sought-after treasures today. Since tourmalines from Malawi with avivid yellow colour, known as 'canary tourmalines', came into the trade, thecolour yellow, which was previously very scarce indeed, has been very wellrepresented in the endless spectrum of colours boasted by the 'gemstone of therainbow'.

Yet the tourmaline has even more names: stones with two coloursare known as bicoloured tourmalines, and those with more than two as multicolouredtourmalines. Slices showing a cross-section of the tourmaline crystal are alsovery popular because they display, in a very small area, the whole of theincomparable colour variety of this gemstone. If the centre of the slice is redand the area around it green, the stone is given the nickname 'water melon'. On the other hand, if the crystal isalmost colourless and black at the ends only, it is called a 'Mohrenkopf', (resembling a certain kind of cake popular inGermany).

Tourmalines are found almost all over the world. There are majordeposits in Brazil, Sri Lanka andSouth and south-west Africa. Other finds have been made in Nigeria, Zimbabwe,Kenya, Tanzania, Mozambique,Madagascar, Pakistan and Afghanistan. Tourmalines are alsofound in the USA, mainly in California and Maine.Although there are plenty of gemstone deposits which contain tourmalines, goodqualities and fine colours are not often discovered among them. For thisreason, the price spectrum of the tourmaline is almost as broad as that of itscolour.

The 'aschentrekker'

It is not only designers who love the tourmaline on account of itsinspiring variety of colour. Scientists too are interested in it because of itsastonishing physical qualities, for tourmalines can become electrically chargedwhen they are heated and then allowed to cool. Then, they have a positivecharge at one end and a negative one at the other. This is known as'pyro-electricity', derived from the Greek word 'pyr', meaning fire. Thegemstone also becomes charged under pressure, the polarity subsequentlychanging when the pressure is taken off. When the charge changes, thetourmaline begins to oscillate, similar to a rock crystal but much morepronouncedly. The Dutch, who were the first to bring the tourmaline to Europe, were familiar with this effect a long time beforeit was able to be provided with a scientific explanation. They used a heatedtourmaline to draw up the ash from their meerschaum pipes, and called thegemstone with the amazing powers an 'aschentrekker'.

In the fascinating world of gemstones, the tourmaline is veryspecial. Its high availability and its glorious, incomparable colour spectrummake it one of our most popular gemstones - and apart from that, almost everytourmaline is unique.

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