有声英文阅读-钻石

Diamonds
钻石

     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 1 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 2 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.
     

     钻石既珍贵稀缺，又美丽晶莹，也用途很广。钻石是自然界里最坚硬的物质。这就意味着钻石能划破任何物体的表面。只有另一块钻石才能在一块钻石上留下轻微的划痕。
     钻石（金刚石）由纯碳所组成。在一切生物中，包括动物和植物，都含有碳。地球上的绝大部分碳都是来自从前的生物。
     科学家们都知道，只有在极高的高温和高压这两个条件结合起来的情况下，才能把碳转化成金刚石（钻石）。这种极其高的高温和高压只有在地球内部深处，溶化了的岩石成极热的液体状态下才能存在。据认为在数百万年以前，这种液态的物质冷却以后，纯碳就变成了钻石结晶。
     在全世界只有四个地区发现有大量的钻石：
     第一个著名产区就是印度，这里在成千上万年前就发现有钻石。在17世纪从欧洲到印度来的旅行者们从印度带回去一些美丽的宝石，于是钻石就成了欧洲各国的国王和王后们最珍爱的宝物了。
     到了18世纪20年代在巴西发现了钻石，这一发现恰逢其时。因为印度的宝石经过了2500多年的开采，采到最后已经快被采光了。
     到了19世纪，在俄国和南非也发现了两个重要的钻研矿区。今天大部分工业用金刚石都产自俄国。作珍宝装饰用的绝大部分钻石都产自南非。在开采出来的钻石总数当中只有25%的钻石，品级够得上可以打磨成珍宝。
     印度的钻石绝大部分是在河床中发现的。众都是从河床底上捧起一大把一大把的砾石，然后从中挑拣出钻石来。这些钻石很可能在两万年前，整个地球各地都被大片大片的冰川所覆盖着的时期，从钻石生盛典的地方顺着冰川流到印度来的。
     可是，今天绝大多数的钻石都不是在河床上找到的；今天的钻石都是从地球内部很深的地方，从被称为岩筒的管状矿脉的矿井中开采出来的。专家们认为这些岩筒都是火山的一部分，是在溶岩从地壳的裂缝中挤压到上面来的时候形成的。里面含有钻石的坚硬的矿石叫蓝脉矿。