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每次遇到这种矿石类的文章就头晕，感觉读着读着就不知道文章到底在讲什么，要看好几遍才能看出个所以然来。
试了做了一遍分析，但分析完之后，自己对文章的结构还是模糊的。苦恼啊，我该怎么弄这种文章呢？==
GWD6-Q23 to Q26:
Diamonds are almost impossible to detect directly because they are so rare（提出这样一个问题，引出下文，相当于主题句）: very rich kimberlite pipes, the routes through which diamonds rise, may contain only three carats of diamonds per ton of kimberlite. （引号后面的内容是对前一句的解释，可略看，但不可以不看） Kimberlite begins as magma in Earth’s mantle (the layer between the crust and the core).As the magma smashes through layers of rock, it rips out debris, creating a mix of liquid and solid material. Some of the solid material it brings up may come from a so-called diamond-stability field, where conditions of pressure and temperature are conducive to the formation of diamonds.If diamonds are to survive, though, they must shoot toward Earth’s surface quickly.Otherwise, they revert to graphite or burn.（解释钻石是怎么形成的，可略读）Explorers seeking diamonds look for specks（标志）of “indicator minerals” peculiar to the mantle but carried up in greater quantities than diamonds and eroded out of kimberlite pipes into the surrounding land. （提出一个寻找钻石的方法，之后是对该方法的补充） The standard ones are garnets, chromites, and ilmenites.One can spend years searching for indicators and tracing them back to the pipes that are their source; however, 90 percent of kimberlite pipes found this way are barren of diamonds, and the rest are usually too sparse to mine.
In the 1970’s the process of locating profitable pipes was refined
（修改） by focusing on the subtle（微妙的） differences between the chemicalsignatures of indicator minerals found in diamond-rich pipes as opposed to those found in barren pipes.（2p的主题句，后面的example就是围绕这句话展开论述）For example, G10 garnets, atype of garnet typically found in diamond-rich pipes,are lower in calcium and higher in chrome than garnets from barren pipes.Geochemists John Gurney showed that garnets with this composition were formed only in the diamond-stability field; more commonly found versions came from elsewhere in the mantle.Gurney also found that though ilmenites did not form in the diamond-stability field, there was a link useful for prospectors:when the iron in ilmenite was highly oxidized, its source pipe rarely contained any diamonds.He reasoned that iron took on more or less oxygen in response to conditions in the kimberlitic magma itself—mainly in response to heat and the available oxygen. When iron became highly oxidized, so did diamonds; that is, they vaporized into carbon dioxide.
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GWD6-Q23:
The primary purpose of the passage is to
A.discuss an objection to Gurney’s theories about the uses of indicator minerals
B.explore the formation of diamonds and the reasons for their scarcity
C.analyze the importance of kimberlite pipes in the formation of diamonds
D.define the characteristics of indicator minerals under differing conditions
E.explain a method of determining whether kimberlite pipes are likely to contain diamonds
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GWD6-Q24:
Each of the following is mentioned in the passage as a difference between G10 garnet and other versions of garnet EXCEPT
A.level of oxidation
B.commonness of occurrence
C.chemical signature
D.place of formation
E.appearance in conjunction with diamonds
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GWD6-Q25:
The passage suggests that the presence of G10 garnet in a kimberlite pipe indicates that
A.the pipe in which the garnet is found has a 90% chance of containing diamonds
B.the levels of calcium and chrome in the pipe are conducive to diamond formation
C.the pipe passed through a diamond-stability field and thus may contain diamonds
D.any diamonds the pipe contains would not have come from the diamond-stability field
E.the pipe’s temperature was so high that it oxidized any diamonds the pipe might have contained
正确选项的选择基于对G10 garnets这一段的了解之上，错误选项都可以简单的排除掉。
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GWD6-Q26:
According to the passage, Gurney refined the use of ilmenites in prospecting for diamonds in which of the following ways?
A.He found that ilmenites are brought up from the mantle by kimberlite pipes and erode out into the surrounding land in greater quantities than diamonds.
B.He found that since ilmenites do not form in the diamond-stability field, their presence indicates the absence of diamonds.
C.He showed that highly oxidized iron content in ilmenites indicates a low survival rate for diamonds.
D.He found that when the iron in ilmenites is highly oxidized, conditions in the magma were probably conducive to the formation of diamonds.
E.He showed that ilmenites take on more or less oxygen in the kimberlite pipe depending on the concentration of diamonds.
题目看起来较难，其实选出正确的答案并不难，只要对ilmenites这一段有大致的了解，就可以轻松地排除掉A,B,D,E.
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发表于 2010-6-1 09:21:18
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