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# GMAT Prep RC: Diamonds are almost impossible to detect

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GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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22 Jun 2016, 09:58
2
4
Question 1
00:00

based on 363 sessions

47% (03:03) correct 53% (03:32) wrong

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Question 2
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based on 352 sessions

51% (01:27) correct 49% (01:21) wrong

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Question 3
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based on 345 sessions

74% (01:08) correct 26% (01:27) wrong

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Question 4
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based on 320 sessions

83% (01:09) correct 17% (01:12) wrong

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New GMAT Prep RC Project: 1 RC Every day. Don't forget to time yourself with the stopwatch below to earn kudos.

Diamonds are almost impossible to detect directly because they are so rare: very rich kimberlite pipes, 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.

1) 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

2) 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

3) 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

4) 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.

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Re: GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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22 Jun 2016, 09:59
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Re: GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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22 Jun 2016, 11:06
3
Timer : 10min 43sec

1) The primary purpose of the passage is to
A. discuss an objection to Gurney’s theories about the uses of indicator minerals
Incorrect, as Gurney's theories are discussed only in the last 10-15 lines of the Paragraph.

B. explore the formation of diamonds and the reasons for their scarcity
Incorrect, no details regarding formation of diamonds is given.

C. analyze the importance of kimberlite pipes in the formation of diamonds
Incorrect, the passage describes relation between the kimberlite pipes and the diamond. It does state the importance anywhere.

D. define the characteristics of indicator minerals under differing conditions
Incorrect, Indicator minerals surface only in the second half of the passage. Also the characteristics of Indicator mineral are not discussed in "Differing Conditions"

E. explain a method of determining whether kimberlite pipes are likely to contain diamonds
Correct, the passage starts with the discussion of Kimberlite pipe, their formation, their characteristics and their relation with "Indicator Minerals".

2) 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 - Correct, used to describe properties of ilmenites
B. commonness of occurrence - Incorrect, a type of garnet typically found in diamond-rich pipes
C. chemical signature - Incorrect, are lower in calcium and higher in chrome than garnets from barren pipes.
D. place of formation - Incorrect, Geochemists John Gurney showed that garnets with this composition were formed only in the diamond-stability field
E. appearance in conjunction with diamonds - Incorrect, a type of garnet typically found in diamond-rich pipes

3) 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- Incorrect, 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.No reference of G10 w.r.t. 90%.

B. the levels of calcium and chrome in the pipe are conducive to diamond formation - Incorrect, are lower in calcium and higher in chrome than garnets from barren pipes. Passage and Choice B mean different.

C. the pipe passed through a diamond-stability field and thus may contain diamonds. Correct, Geochemists John Gurney showed that garnets with this composition were formed only in the diamond-stability field;

D. any diamonds the pipe contains would not have come from the diamond-stability field. Incorrect

E. the pipe’s temperature was so high that it oxidized any diamonds the pipe might have contained. Incorrect, the oxidation is referred to Ilemnite and not Garnet.

4) 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. Correct, When iron became highly oxidized, so did diamonds; that is, they vaporized into carbon dioxide.
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.

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Re: GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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23 Jun 2016, 06:42
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Interesting passage , all correct in 7 mins 40 seconds . Took 2 mins and 30 seconds to read the passage .
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Re: GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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04 Jun 2017, 17:46
Took me 10 mins 40 seconds overall. All correct !
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Re: GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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04 Jul 2017, 22:55
Took 6 mins 31 secs , 1 wrong
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GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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06 Nov 2017, 11:00
Took me 8 mins to complete.

Got 1 wrong.
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Re: GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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07 Jun 2018, 09:14
I am usually good with RCs but this one killed me. I am never going to a diamond store again.
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Re: GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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07 Jun 2018, 20:46
Took 8 minutes and got 2 wrong.
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Re: GMAT Prep RC: Diamonds are almost impossible to detect  [#permalink]

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18 Jun 2018, 23:43
Nice passage. Made a careless error in the first question. Rest all were correct
Re: GMAT Prep RC: Diamonds are almost impossible to detect &nbs [#permalink] 18 Jun 2018, 23:43
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