They are older than the dinosaurs, older than nearly everything else on earth. They have been used to cut 1 kings and queens. Famed 2 their flashing beauty, diamonds are the hardest substances in existence and among the most useful. They offer a 3 of the earth.
Most diamonds were formed billions of years ago in 4 About 100 miles underground, the mantle puts extreme heat and pressure on carbon, the common black substance in coal and pencils. These forces turn black carbon into clear diamond crystal. As the crystal grows, 5 other chemicals inside, creating a type of space capsule from the inner earth.
How did diamonds arrive on the earth’s surface? They were 6 boiling eruptions of melted rock hundreds of millions of years after they were formed. These eruptions were smaller but much more powerful 7 modern volcanoes. In 1872 scientists discovered that these ancient volcanoes 8 bringing diamonds from deep inside the earth up through rocky “pipes” to the surface.
But diamonds have also been found far from these places. Volcanic rock 9 over time, and diamonds are carried far away. They’ve been spotted in the sand and gravel in parts of India 10
Today, diamonds are mined on every continent except Europe and Antarctica. South Africa once shone as the diamond capital of the world: a huge rush was sparked by a 15-year-old’s lucky diamond find in a bed of gravel in the 1860s. Now Australia is the king of 11 39% of the gems found each year.
Digging for diamonds 12 an expensive and exhausting operation. Miners may dig through about 250 tons of rock to find just one stone. Furthermore, only a fraction of the 10 tons of natural diamonds mined each year are perfect enough to be fashioned into necklaces, pins and rings. 
The 80% of diamonds that are too flawed for jewels are 14 still valuable. These stones, called industrial diamonds, are used to create everything from protective eyeglasses to computer chips.
Most businesses no longer buy natural diamonds because of their being costly, but have instead switched to synthetic diamonds. In 1955 researchers at General Electric figured out how to turn 15 diamonds cheaper and easier to shape for products ranging from golf clubs to supercomputers, and even to spaceships!
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The writer wants to emphasize the fact the diamonds are propelled violently to the earth’s surface. Given this purpose, which choice would work best?CorrectIncorrect
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Furthermore, only a fraction of the 10 tons of diamonds mined each year are perfect.
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