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Diamonds

Some of the earliest diamonds known came from India. In the eighteenth century they were found in Brazil, and in 1866, huge deposits were found near Kimberley in South Africa. Though evidence of extensive diamond deposits has recently been found in Siberia, the continent of Africa still produces nearly all the world’s supply of these stones.

The most valuable diamonds are large, individual crystals of pure crystalline carbon. Less perfect forms, known as ‘boart’ and ‘carbonado’ are clusters of tiny crystals. Until diamonds are cut and polished, they do not sparkle like those you see on a ring-they just look like small, blue-grey stones.

In a rather crude form, the cutting and polishing of precious stones was an art known to the Ancient Egyptians, and in the Middle Ages it became widespread in north-west Europe. However, a revolutionary change in the methods of cutting and polishing was made in 1476 when Ludwig Van Berquen of Bruges in Belgium invented the use of a swiftly revolving wheel with its edge faced with fine diamond powder. The name ‘boart’ is given to this fine powder as well as the natural crystalline material already mentioned. It is also given to badly flawed or broken diamond crystals, useless as jewels, that are broken into powder for grinding purposes, the so-called ‘industrial’ diamonds.

Diamond itself is the only material hard enough to cut and polish diamonds-though recently, high-intensity light beams called lasers have been developed which can bore holes in them. It may be necessary to split or cleave the large stones before they are cut and polished. Every diamond has a natural line of cleavage, along which it may be split by a sharp blow with a cutting edge.

A fully cut ‘brilliant’ diamond has 58 facets, or faces, regularly arranged. For cutting or faceting, the stones are fixed into copper holders and held against a wheel, edged with a mixture of oil and fine diamond dust, which is revolved at about 2,500 revolutions a minute. Amsterdam and Antwerp, in Holland and Belgium respectively, have been the centre of the diamond cutting and polishing industry for over seven centuries.

The jewel value of brilliant diamonds depends greatly on their colour, or ‘water’ as it is called. The usual colours of diamonds are white, yellow, brown, green, or blue-white; the blue-white brilliants are the stones of the ‘finest water’ and so command the highest prices. During their formation. some diamonds absorb metallic oxides from the surrounding rocks and take on their colour. Thus black, red and even bright pink diamonds have occasionally been found.

The trade in diamonds is not only in the valuable gem stones but also in the industrial diamonds mentioned above. Zaire produces 70% of such stones. They are fixed into the rock drills used in mining and civil tools engineering, also for edging band saws for cutting stone. Diamond-faced tools are used for cutting and drilling glass and fine porcelain, and for dentists' drills. They are used as bearings in bearings in watches and other finely balanced instruments. Perhaps you own some diamonds without knowing it-in your wristwatch!

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You can memorize words in an efficient way if you pronounce them reasonably. Say words correctly, and you will learn them easily. Correct pronunciation means correct spelling of the words. English spelling is not good to guide its pronunciation. But spelling and pronunciation have closed relationship. They match each other perfectly. Sometimes we can pronounce a word according to its spelling. English pronunciation can also guide its spelling. This is a two-way communication.
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五花八门(9)

The Rainy Day 雨天(mp3)
A Grain of Sand 一粒沙子(mp3)
A Forever Friend 永远的朋友(mp3)
Money
Diamonds
Canning food
The Olympic Games
Auction sales
The planemakers
Dreams-what do they mean?
To be or not to be a vegetarian
Making leather
Cat
The history of chemistry
Electric fish
Dried food
The United Nations
Pottery
Pasteurization
Modern surgery

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