In the English language, the two words “carat” and “karat” are pronounced the same way, but they are quite different in meaning. This difference is of great importance to a jeweller, and of some importance to us as students of geology as well. The word “carat”—spelled with a “c”—refers to a unit of weight used to classify diamonds and other gemstones. One carat equals 200 milligrams, or a hundred-fortieth of an ounce. This unit of measurement dates back 2,500 years to ancient India, where diamonds were first discovered and used as decorative objects. Diamonds were then classified by comparing them to the seed of a carob plant, similar to what we would call a locust three today. These seeds were chosen because their weight varied very little from seed to seed. The weight of one of these seeds was determined to be equal that of a one-carat diamond. The diamonds found in most jewelry stores are typically less than a carat in weight. For this reason, a carat is divided into points, with 100 of these smaller units to the carat. Therefore, a diamond weighing 50 points would be one half carat in weight.
On the other hand, a karat—spelled with a “k”—is a unit of purity, which is most often used to describe gold and platinum or white gold. Each karat represents 1/24th of the whole. Twenty-four karat gold is the metal in its purest from. But because of its softness, and to some extent its value, gold is usually mixed with another metal like copper or silver make jewelry. So, if a piece of jewelry is made of metal that is 18 parts gold and 6 parts copper, that is what we call 18-karat gold.
Where did such a strange unit of purity come from? It turns out that the answer to this question reveals an interesting historical connection between carat as a unit of weight and karat as a unit of purity. The fact that they are pronounced the same way is not at all coincidental. There was a German gold coin called a mark, which was common about a thousand years ago. It weighed 24 carats or about 4.8 grams. The purity of the gold in the corn was expressed as the number of carats of gold present in this 24-carat coin. According to the lecture why was the weight of the carob seed first used as a standard for diamonds? C A Carob seeds were plentiful B Carob seeds were about the same size as diamonds. C Carob seeds were all of about the same weight D Carob seeds weighed about 200 milligrams.
What is emphasized in the lecture as the main difference between a carat and a karat? C A One karat equals 24 carats B A karat is used for gold while a carat is used for gemstones. C They are used to measure different characteristics. D One carat was used much earlier than the other.
According to the professor, why is 24-karat gold seldom used to make jewelry? B A It s too difficult to form it into shaoes. B It isn’t hard enough. C It is too heavy. D It cannot be made perfectly pure.
Which of the following can be inferred from the lecture? C A The German mark was a pure gold coin. B The German mark was equal in value to a 24-carat diamond. C The German mark weighed as much as a 24-carat diamond. D The German’s used coins made of gold mixed with other metals.
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发表于 2003-7-29 14:41:00
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