【GMAT考满分阅读RC题库】Diamonds are almost impossible to detect directly _真题_答案

GWD - 阅读RC - 51

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Diamonds are almost impossible to detect directly because they are so rare: very rich kimberlitepipes, the routes through which diamonds rise, may contain only three carats of diamonds per ton of kimberlite. 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. Explorers seeking diamonds look for specks 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. 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 by focusing on the subtle differences between the chemical signatures of indicator minerals found in diamond-rich pipes as opposed to those found in barren pipes. For example, G10 garnets, a type 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.

Each of the following is mentioned in the passage as a difference between G10 garnet and other versions of garnet EXCEPT

Alevel of oxidation
Bcommonness of occurrence
Cchemical signature
Dplace of formation
Eappearance in conjunction with diamonds

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正确答案: A

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shallylee

错选了E
E中的appreance不是“外表”，而是“出现”的意思
当时排除了A是看到文章最后那里说了很多关于oxidation的东西，以为是mention了，但是其实那里已经不再是在讲G10了，而是在讲另外一种铁矿了。

2016-05-30 10:18:14 IP属地：湖南举报

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在中的Amour 回复 shallylee

跟我一样TAT

2017-10-31 10:17:42 IP属地：广东举报

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杀G上730给我冲回复 shallylee

appearance亲..来自2019年末的凝视

2019-11-21 10:04:22 IP属地：局域网举报

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lethe415

B. commonness of occurrence -----more commonly 【found 】versions came from elsewhere in the mantle.
C. chemical signature----- are lower in calcium and higher in chrome than garnets from barren pipes
D. place of formation ---garnets with this composition were 【formed】 only in the diamond-stability field
E.appearance in conjunction with（伴随着） diamonds---a type of garnet typically found in diamond-ri

2016-07-25 01:02:23 IP属地：安徽举报

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GenFriedrich

解释中，答案D 和 E标注的位置好像是放反了。

2017-01-20 17:59:31 IP属地：北京举报

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小糖同学

觉得这题出得很好，第一次做的时候觉得云里雾里，其实回头看答案就在字里行间，然后同义改写要看明白~~

2016-09-10 17:41:37 IP属地：湖北举报

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小雨家的宝宝

哇，每个选项在原文中都好抽象……

2016-11-27 21:11:56 IP属地：局域网举报

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TuLiP

appearance 这里应该是出现的意思吧

2012-12-03 21:11:17 IP属地：保留地址举报

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isominia

A主要iron的level of oxidation啊

2013-07-16 09:23:57 IP属地：江苏举报

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葱葱爱豹子头

把EXCEPT看掉的怕是只有我一个人了………………

2019-07-27 15:42:13 IP属地：北京举报

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sea星星一定700 回复葱葱爱豹子头

我也觉得自己的眼睛很该反省反省了):

2019-08-23 15:14:25 IP属地：北京举报

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学员Y8NzxL 回复葱葱爱豹子头

还有我，这么简单的一道题，回头还一顿分析，结果才发现except

2023-05-27 16:54:44 IP属地：上海举报

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GravityYin

看到EXCEPT很关键！
Oxidation（氧化）是第二种方法涉及到：关于ilmenite（钛铁矿）中铁的氧化。

2015-08-19 15:23:28 IP属地：局域网举报

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我要考mf

啥笔题

2020-06-05 12:31:06 IP属地：局域网举报

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正确率： 39%

难度：

选择材料题号

GWD

GWD
PREP07 Test 1
PREP07 Test 2
PREP2012
OG16
OG17
PREP08 Test 1
PREP08 Test 2
Manhattan
Magoosh
OG18
OG18-数学分册
OG18-语文分册
OG19
OG19-语文分册
OG19-数学分册
OG20
OG20-语文分册
OG20-数学分册

SET 1

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