有聲英文閱讀-鉆石

所屬教程:有聲英文閱讀

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Diamonds
鉆石

Diamonds are rare, beautiful, and also quite useful. They are the hardest substance found in nature. That means a diamond can cut any other surface. And only another diamond can make a slight cut in a diamond.

Diamonds are made from carbon. Carbon is found in all living things, both plant and animal. Much of the carbon in the earth comes from things that once lived.

Scientists know that the combination of extreme heat and pressure changes carbon into diamonds. Such heat and pressure exist only in the hot, liquid mass of molten rock deep inside the earth. It is thought that millions of years ago this liquid mass pushed upward through cracks in the earth's crust. As the liquid cooled, the carbon charged into diamond crystals.

There are only four areas where very many diamonds have been found.

The first known area was in India, where diamonds were found thousands of years ago. In the 1600's, travelers from Europe brought back these beautiful stones from India. Diamonds became very popular with the kings and queens of Europe.

In the 1720's, diamonds were discovered in Brazil. This discovery came at a good time, too. India's supply of diamonds was finally running out after 2,500 years of mining the stones.

In the 1800's, two other important areas were found in Russia and South Africa. Today, most diamonds used in industry come from Russia. Most diamonds used as gems come from South Africa. Only 25 percent of all diamonds mined are good enough for cutting into gems.

Most of the diamonds in India were found in stream beds. People would pick up handfuls of gravel from the bottom of the streams and sort out the diamonds. These diamonds were probably carried from where they were formed to India by great sheets of moving ice that covered parts of the earth 20,000 years ago.

Most diamonds today are not found in stream beds, however. They are mined from rock formations deep inside the earth called pipes. Scientists believe that these are parts of volcanoes that were formed when molten rock pushed upward through the earth's crust. The hand rock in which diamonds are found is called blue ground.

鉆石既珍貴稀缺，又美麗晶瑩，也用途很廣。鉆石是自然界里最堅硬的物質(zhì)。這就意味著鉆石能劃破任何物體的表面。只有另一塊鉆石才能在一塊鉆石上留下輕微的劃痕。

鉆石（金剛石）由純碳所組成。在一切生物中，包括動物和植物，都含有碳。地球上的絕大部分碳都是來自從前的生物。

科學家們都知道，只有在極高的高溫和高壓這兩個條件結(jié)合起來的情況下，才能把碳轉(zhuǎn)化成金剛石（鉆石）。這種極其高的高溫和高壓只有在地球內(nèi)部深處，溶化了的巖石成極熱的液體狀態(tài)下才能存在。據(jù)認為在數(shù)百萬年以前，這種液態(tài)的物質(zhì)冷卻以后，純碳就變成了鉆石結(jié)晶。

在全世界只有四個地區(qū)發(fā)現(xiàn)有大量的鉆石：

第一個著名產(chǎn)區(qū)就是印度，這里在成千上萬年前就發(fā)現(xiàn)有鉆石。在17世紀從歐洲到印度來的旅行者們從印度帶回去一些美麗的寶石，于是鉆石就成了歐洲各國的國王和王后們最珍愛的寶物了。

到了18世紀20年代在巴西發(fā)現(xiàn)了鉆石，這一發(fā)現(xiàn)恰逢其時。因為印度的寶石經(jīng)過了2500多年的開采，采到最后已經(jīng)快被采光了。

到了19世紀，在俄國和南非也發(fā)現(xiàn)了兩個重要的鉆研礦區(qū)。今天大部分工業(yè)用金剛石都產(chǎn)自俄國。作珍寶裝飾用的絕大部分鉆石都產(chǎn)自南非。在開采出來的鉆石總數(shù)當中只有25%的鉆石，品級夠得上可以打磨成珍寶。

印度的鉆石絕大部分是在河床中發(fā)現(xiàn)的。眾都是從河床底上捧起一大把一大把的礫石，然后從中挑揀出鉆石來。這些鉆石很可能在兩萬年前，整個地球各地都被大片大片的冰川所覆蓋著的時期，從鉆石生盛典的地方順著冰川流到印度來的。

可是，今天絕大多數(shù)的鉆石都不是在河床上找到的；今天的鉆石都是從地球內(nèi)部很深的地方，從被稱為巖筒的管狀礦脈的礦井中開采出來的。專家們認為這些巖筒都是火山的一部分，是在溶巖從地殼的裂縫中擠壓到上面來的時候形成的。里面含有鉆石的堅硬的礦石叫藍脈礦。