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Diamonds are so hard that only _____ can cut it.
A．a man who knows all about diamonds
B．diamond-edged tools
C．a special cutter
D．diamond cutter
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They're diamonds!
For hundreds of years men have risked their lives searching for diamonds. To many the discovery of this glittering treasure has seemed more important than the discovery of new lands. Fairy stories tell of brave knights who battled fierce dragons and evil wizards to win kingdom rich with diamonds. In the Tower of Ion- don in England, there is a very special room protected by guards. There, inside a thick glass case, are jeweled crowns once worn by kings and queens. People from all over the world come to see the shimmering diamonds and other precious stones that shine from behind the glass.
Most diamonds seem to flash with a kind of white fire. But there are diamonds that sparkle in other colors, too. Sometimes diamonds are discovered in gravel at the bottom of rivers and streams. (To get these diamonds, the gravel is sucked up through giant hoses that act like vacuum cleaners.) Diamonds are found in rivers, on land, and in great stretches of hot desert sand. A few small ones are even found or near meteorites that strike the ground from outer space.
But most diamonds are found in rocks deep inside the diamond mines of Africa. The diamonds were made millions and millions of years ago when flaming volcanoes melted a mineral called carbon which was a part of these rocks. Gigantic earthquakes shook the rock and pressed them tightly together. The hot melted carbon in the rock squeezed at the same time--squeezed so tightly that by the time it cooled, it had changed into the lovely hard gems called diamonds.
To get at these valuable diamond rocks, workers ride in an elevator that goes down and down into the blackness far below the ground. Tunnels connect this deep shaft with the openings--called pipes--inside the ancient volcanoes.
When they are first dug from the mines, diamonds don't glitter or sparkle as they do when we see them in rings or other jewelry. They look more like dull bits of glass. A man who knows all about diamonds--a diamond cutter--must cut them just right. Diamonds are so hard that nothing can cut them except the edge of an- other diamond.
Using his diamond-edged tools, the diamond cutter carefully removes tiny pieces so that the diamond will have many sharp edges and smooth surfaces--like little windows. It is because of these shaft edges and smooth surfaces that the diamond reflects light, sparkles and flashes with tiny bursts of color, and seems almost ablaze with fire. Diamond cutters often use diamond saws. The fine powder--diamond dust--that is left after the sa- wing is done can be used in a kind of sandpaper to polish the sparking gems.
Not all diamonds are clear enough or pretty enough or large enough to be made into jewelry. But because they are so hard, they can be used for other things, such as points for drills and needles for record player. These diamonds are called industrial diamonds. Some of them are man made. Carbon is heated until it is hot and then squeezed. If men ever learn how to make it hot enough and to squeeze it tightly enough, they will probably be able to make big diamonds. Then maybe diamonds will be cheap enough to use as buttons on your shirt or coat! (610)
The following are the characters of diamonds EXCEPT ______.
A．they sparkle and glitter in the light
B．they are very hard
C．they are very valuable
D．they are tiny
At first this did not seem like a particularly hard task. Scientists began to try making synthetic diamonds towards the end of the eighteenth century. It was at this time that a key scientific fact was discovered: diamonds are a form. of carbon, which is a very common element. Graphite, the black mineral that is used for the lead in your pencil, is made of it, too. The only difference, we know today, is that the carbon atoms have been packed together in a slightly different way. The chemists were fired with enthusiasm: Why not change a cheap and plentiful substance, carbon, into a rare and expensive one, diamond？
You have probably heard about the alchemists who for centuries tried to turn plain lead or iron into gold. They failed because gold is completely different from lead or iron. Transforming carbon into diamonds, however, is not illogical at all. This change takes place in nature, so it should be possible to make it happen in the laboratory.
It should be possible, but for one hundred and fifty years efforts failed. During this period, none the less, several people believed that they had solved the diamond riddle. One of these was a French scientist who produced crystals that seemed to be the real thing. After the man's death, however, a curious rumour began to go the rounds. The story told that one of the scientist's assistants had simply put tiny pieces of genuine diamonds into the carbon mixture. He was bored with the work, and he wanted to make the old chemist happy.
The first real success came more than sixty years later in the laboratories of the General Electric Company. Scientists there had been working for a number of years on a process designed to duplicate nature's work. Far below the earth's surface, carbon is subjected to incredibly heavy pressure and extremely high temperature. Under these conditions the carbon turns into diamonds. For a long time the laboratory attempt failed, simply because no suitable machinery existed. What was needed was some sort of pressure chamber in which the carbon could be subjected to between 800,000 and 1,800,000 pounds of pressure to the square inch, at a temperature of between 200°F and 2,200°F.
Building a pressure chamber that would not break under these conditions was a fantastically difficult feat, but eventually it was done. The scientists eagerly set to work again. Imagine their disappointment when, even with this equipment, they produce all sorts of crystals, but no diamonds. They wondered if the fault lay in the carbon they were using, and so they tried a number of difficult forms. They failed again and again but went on working. The idea was then brought forward that perhaps the carbon needed to be dissolved in a melted metal. The metal might act as a catalyst, which means that it helps a chemical reaction to take place more easily.
This time the carbon was mixed with iron before being placed in the pressure chamber. The pressure was brought up to 1,100,000 pounds to the square inch and the temperature to 900℉. At last the chamber was opened. A number of shiny crystals lay within. These crystals scratched glass, and even diamonds. Light waves passed through them in the same way as they do through diamonds. Carbon dioxide was given off when the crystals were burned. Their density was just 3.5 grams per cubic centimeter, as is true of diamonds. The crystals were analyzed chemically. They were finally studied under X-rays, and there was no longer room for doubt. These jewels of the laboratory were not like diamonds; they were diamonds. They even had the same atomic structure.
The main idea of Paragraph 2 is that______.
A．making artificial diamonds didn't seem very difficult at first sight
B．scientists began to try making synthetic diamond in the late 1700s
C．scientists discovered diamonds are a form. of carbon, a common element
D．the discovery of the diamonds' constitute impelled scientists to make a synthetic one
Had he not been so busy taking the diamonds, he ______ the blow.
A．would feel
B．had been feeling
C．had felt
D．would have felt
Transforming carbon into diamonds in the laboratory is______.
A．more illogical than turning plain lead or iron into gold
B．less logical than turning plain lead or iron into gold
C．not so illogical as turning plain lead or iron into gold
D．as illogical as turning plain lead or iron into gold
The powder-like diamonds could be among the oldest things in the 【C2】______ , said Roy Lewis, senior research associate at the University of Chicago.
The diamonds may 【C3】______ clues about the chemistry of stars, and if scientists can determine how they formed, that could suggest better ways of manufacturing tiny diamonds for 【C4】______ purposes, he said.
"It's quite possible that nature is doing it more 【C5】______ than we've been doing it," he said. "So maybe we've got something to learn."
The new find is 【C6】______ , said John Wood, staff scientist at the Harvard-Smithsonian Centre for Astrophysics. Although diamonds have been found before in meteorites, they were formed relatively recently 【C7】______ the shock of impact, he said in a telephone interview.
But Wood said the new report made him "quite sure" the newly found diamonds are older than the sun.
Lewis said researchers never expected to find diamonds when they started 【C8】______ a stone-like meteorite that had plunged into Mexican cornfield in 1969.
They were studying an unusual carbon dust in the meteorite, and to purify the sample they went though several steps to dissolve other materials. They expected the sample to remain black through the purification, but to their surprise in the final step it turned 【C9】______ .
Lewis said they believed the final stage had dissolved the carbon they wanted to study. But tests showed that the white residue was in fact made of carbon. Other tests found that it contained an unusual combination of forms of the gas xenon, 【C10】______ that it came from outside the solar system.
Still another battery of tests 【C11】______ the residue as diamond dust, so fine that a row of 20,000 grains would extend about the 【C12】______ of a human hair.
The researchers also found diamonds in three other meteorites, Lewis said. Tests showed all four meteorites were as old as the solar system, and that the embedded diamonds did not form. within the meteorite 【C13】______ of collisions.
So the diamonds must have 【C14】______ somewhere else before the meteorites formed, making them as old or older than the solar system.
The diamonds may have formed in the upper atmosphere of a star in the late "red giant" stage, where the temperature and abundance of hydrogen could 【C15】______ diamonds to form. as carbon gas condenses.
【C1】
A．searching for
B．observing
C．studying
D．discussing
The Origin of Diamonds
Carbon is one of the most common elements in the world, and is one of the four essentials for the existence of life. Humans are more than 18-percent carbon. When occurring in nature, carbon exists in three basic forms, of which diamond is an extremely hard, clear crystal.
Diamonds form. about 161 km below the Earth's surface, in the molten rock of the Earth's mantle, which provides the right amounts of pressure and heat to transform. carbon into a diamond. In order for a diamond to be created, carbon must be placed under at least 435,113 pounds per square inch (psi) of pressure at a temperature of at least 400 Celsius. If conditions drop below either of these two points, graphite will be created. At depths of 150 km or more, pressure builds to about 725,189 psi and heat can exceed 1,200 C.
Kimberlite Pipes
Most diamonds that we see today were formed millions (if not billions) of years ago. Powerful magma eruptions brought the diamonds to the surface, creating kimberlite pipes. Kimberlite is named after Kimberly, South Africa, where these pipes were first found. Most of these eruptions occurred between 1,100 million and 20 million years ago.
Kimberlite pipes are created as magma (岩浆) flows through deep fractures in the Earth. The magma inside the kimberlite pipes acts like an elevator, pushing the diamonds and other rocks and minerals through the mantle and crust in just a few hours. These eruptions were short, but many times more powerful than volcanic eruptions that happen today.
The magma eventually cooled inside these kimberlite pipes, leaving behind conical veins of kimberlite rock that contain diamonds. Kimberlite is a bluish rock that diamond miners look for when seeking out new diamond deposits. The surface area of diamond-bearing kimberlite pipes ranges from 2 to 146 hectares. Diamonds may also be found in river beds, which are called alluvial diamond sites. These are diamonds that originate in kimberlite pipes, but get moved by geological activity. Glaciers and water can also move diamonds thousands of miles from their original location.
Cutting Diamonds
There are special techniques that are used to cut and shape a diamond before it gets to the jewelry store. Diamond cutters first try to remove any impurities or irregularities in the diamond. Sometimes, diamonds have to be sawed with the use of a phosphor-bronze blade or laser. Then the diamond is rubbed by another diamond to create facets-tiny flat spots on the surface. Finally, the diamond is pressed against a rotating polishing wheel to give the diamond its finished look.
Rating Diamonds
Diamonds are judged on several factors that determine their beauty. Most diamonds never reach the consumer market because they are too flawed. Often, these diamonds are used for industrial purposes--as an abrasive, for drill bits or for cutting diamonds and other gems. If you've ever purchased a diamond, you've heard of the "4 Cs:"
1. Cut--This refers to how the diamond has been cut and its geometric proportions. When a diamond is cut, facets are created and the diamond's finished shape is determined.
2. Clarity
A．Y
B．N
C．NG
With prices ______ so much, it's hard for the company to plan a budget.
A．fluctuating
B．waving
C．swinging
D．vibrating
Had they not been working so hard，they______(not achieve)so much.
Richard works really hard,and_____ you.
A.so do
B.so are
C. so did
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