单选题
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They sparkle and glitter
in the light. No other rocks are so hard. They are very valuable. It might cost
thousands and thousands of dollars to buy just one. Most are found in the
ground. The largest ore ever discovered is as big as a man's fist. But most are
tiny.
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 Lon- don in England,
there is a very special room protected by guards. There, inside a thick glass
ease, 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--squee2ed 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 tings 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 another 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
sawing 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)