Diamonds are almost impossible to detect directly because they are so

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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PrakharGMAT, smartguy595, RDhin - may I offer my understanding on these issues?

Q1- The primary purpose of the passage is to

Before going to answer the question, my quick summary to the passage:

Diamonds are rare & hard to detect --> only through "kimberlite pipes" can have diamond --> prev: several ineffective ways to decide which kimberlite pipes have good potential of containing diamond --> later: Gurney's method is more effective.

So now to the answer:

(A)discuss an objection to Gurney's theories about the uses of indicator minerals - incorrect, if any the passage actual supports Gurney's method
(B)explore the formation of diamonds and the reasons for their scarcity - a little bit on the formation of diamond in the first passage, but the rest are all about how to identify rich diamond "kimberlite pipes". Moreover, passage only said diamon are rare - doesn't say anything about why they're rare --> incorrect!
(C)analyze the importance of kimberlite pipes in the formation of diamonds -> very little discuss if any, the important of something at best should be compare with some other similar things, here, I don't see any of other similar thing, diamond is only through "kimberlite pipes" --> so, incorrect!
(D)define the characteristics of indicator minerals under differing conditions --> nope
(E)explain a method of determining whether kimberlite pipes are likely to contain diamonds --> yep, this could be one, 1st passage does talk about Explorers seeking diamonds look for specks of “indicator minerals” and then elaborates more about it, the 2nd passage explore another more effective way to seek diamond in kimberlite pipes --> Correct!

Q2. 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 diamond

This is a tough & tricky one, I need to infer some of the information from the passage:

First, take a look at the 1st passage

“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.

--> so, I can infer that standard characteristic of a possible diamond mine must include garnets
Therefore, there is a conjunction (or good probability of appear together) between garnets & diamond
--> Hence, (E) is out

Second, take a look at the 2nd passage again:

focusing on the subtle differences between the chemical signatures of indicator minerals. --> so (C) is out

garnets with this composition were formed only in the diamond-stability field - it talked about a place of formation (diamond-stability field) --> so (D) is out

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.
- there is an occurrence of garnets in difference pipes but some are more of Ca & Cr than other, could we hence infer that it's talking about how often you can find a type of garnets in different pipes --> so it does talk about commonness of occurrence, however, not too clear --> leave it to 50/50 chance.

So, we only left with A & B!

Read further, the rest of the passage only talk about iron and oxidation, nothing mention about garnets.

So, in all, (A) is more persuasive than B --> choose correct answer A

There is always a difference between the scope of a passage and the reason for writing a certain passage.
B covers everything in the passage, but what it not covers is the intention of the author as to why he/she wrote the passage. Thereby B is the scope and e is the primary purpose of the passage.

I just selected sentences that can help to detect the differences between the 2 types of garnet.

(A)level of oxidation : the passage mentioned the level of occidation as a peculiarity of iron solely.

(B)commonness of occurrence -> Diamonds are almost impossible to detect directly because they are so rare ... garnets with this composition were formed only in the diamond-stability field; more commonly found versions came from elsewhere in the mantle

(C)chemical signature -> by focusing on the subtle differences between the chemical signatures .... For example, G10 garnets, are lower in calcium and higher in chrome than garnets from barren pipes

(D)place of formation -> more commonly found versions came from elsewhere in the mantle

(E)appearance in conjunction with diamond -> garnets with this composition were formed only in the diamond-stability field

Hope it helps !

B says: "explore the formation of diamonds and the reasons for their scarcity".

There is actually no where in the passage that "formation of diamonds" has been explored. The only reference of diamond formation is in regards to "diamond-stability field" (where conditions of pressure and temperature are conducive to the formation of diamonds).

The passage is about kimberlite pipes, how most of them are barren and how some techniques (differences between the chemical signatures of indicator minerals in kimberlite pipes) can help to increase the "hit ratio".

In question 3, I was doubting between options B and C.

The passage suggests that the presence of G10 garnet in a kimberlite pipe indicates that:

B) the levels of calcium and chrome in the pipe are conducive to diamond formation
I discarded this option because the levels of calcium and chrome do not lead to diamond formation. They are rather a signal of diamond formation.

C) the pipe passed through a diamond-stability field and thus may contain diamonds
Support for this option:
"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;..."

Could you please give your opinion on my reasoning for discarding option B?

HI...

it is given in the coloured portion above that G10 are found in diamond rich pipe whereas the other garnet in barren pipe..
so G10 appears in conjunction with diamond..

choice E means G10 appearing along with diamond.
May be one can get confused in literal meaning of APPEARANCE as LOOKS
_________________

Hi lakshya14,



Question 3 asks what does the presence of G10 garnet in a kimberlite pipe indicate. It can be inferred from the lines:
"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;",implying that G10 garnet is found in diamond rich pipes, lower in calcium and higher in chrome, in turn implying that the pipe passed through a diamond-stability field.



I believe your doubt is related to option B. Levels doesn't necessarily mean "high levels" only it could mean low level as well. Option B is incorrect because of the word conducive as it gives a different meaning to the sentence. We can't infer if levels of calcium and chrome in the pipe play a part in diamond formation. We can only infer that one of “indicator minerals” garnets is found in diamond-rich pipes are lower in calcium and higher in chrome than garnets from barren pipes.


Hope This Helps.
Thanks.

Even have doubts regarding first question. I elminated E because of a method, there are more than one methods discussed, I found B better because formation and reason for scarcity is discussed but thats not central idea so eliminated that too. at last I marked D because the first 3 lines introduce indicator minerals discussed later and second para is all about their characteristics. more thoughts plz

Hey GMATNinja and GMATNinjaTwo

can you help to explain the below question? I am not convinced with the answers given in this thread

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 diamond
_________________

Dear Moderators workout, u1983 broall Gnpth

Please add the below question
Source: Practice Exam 4 (mba.com)

Q. Which of the following best describes the primary purpose of the second paragraph of the passage?

(A)It describes a method of diamond formation different from the one described in the first paragraph.
(B)It gives examples of the ways in which a method for locating diamonds may be applied to other gems.
(C)It gives examples of exceptions to the natural phenomenon of diamond formation as described in the first paragraph.
(D)It discusses an improvement to the process of diamond prospecting described in the first paragraph.
(E)It challenges the scientific foundation of the method of diamond prospecting described in the first paragraph.

OA is D, would appreciate if explanation is also provided

Video solution from Quant Reasoning:
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I believe you are referring to the following: He found that since ilmenites do not form in the diamond-stability field, their presence indicates the absence of diamonds.

"ilmenites" is actually an "indicator mineral" so the presence "ilmenites" cannot mean absence of diamonds. As per the passage, the presence of "oxidized" ilmenites would most probably mean absence of diamonds. Look at the following sentence from the passage:

when the iron in ilmenite was highly oxidized, its source pipe rarely contained any diamonds.

Hi Experts / chetan2u / daagh ,

Can you please debrief Q1 (Primary purpose) and in Q2 where can we find appearance in conjunction with diamond.

As mentioned by one of GMAT aspirant that -->

(E) appearance in conjunction with diamond -> garnets with this composition were formed only in the diamond-stability field
Is he correct..??

Actually I am not convinced with it because it talks about composition and its not at all related with APPEARANCE...

Please assist

Marcab

As you said-
There is always a difference between the scope of a passage and the reason for writing a certain passage.

Can you please shed more light on it. How could we make out the reason behind writing the passage.
_________________

Hi,

mikemcgarry, chetan2u, VeritasPrepKarishma, GMATNinja, sayantanc2k

Can you please help with the below question:

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 diamond

Can you help me identify the evidence from the passage to rule out option E ?

Thanks in advance

Dear souvik101990 Skywalker18

Please add the below question
Source: Practice Exam 4 (mba.com)

Q. Which of the following best describes the primary purpose of the second paragraph of the passage?

(A)It describes a method of diamond formation different from the one described in the first paragraph.
(B)It gives examples of the ways in which a method for locating diamonds may be applied to other gems.
(C)It gives examples of exceptions to the natural phenomenon of diamond formation as described in the first paragraph.
(D)It discusses an improvement to the process of diamond prospecting described in the first paragraph.
(E)It challenges the scientific foundation of the method of diamond prospecting described in the first paragraph.

OA is D, would appreciate if explanation is also provided

Could someone comment on Q4 option (B)

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.

Hi GMATNinja CrackVerbalGMAT IanStewart MartyTargetTestPrep GMATGuruNY generis Sajjad1994 bm2201

Shall we reject B only because absence of diamonds is present ?
Low survival rate for diamonds is right word for rarely contained any diamonds

Or is there any other reason to choose C over B?

The options looks so close or am I missing something in the question ?
Refined the use in which of following ways?


Additional query:
they vaporized into carbon dioxide --doesn't they refer to all diamonds ?
E.g. : If i say these items are not available. I don't mean rarely present or present in low quantity but I mean all are not present. Isn't it?
Actually I reject C due to 2 reasons : 1. rarely means hardly any ( almost null) 2. If still some diamonds are present ( even in low quantity) then those still need to be find out.And if it is so, this refined method is not useful . Because it doesn't save efforts in the end .

Experts opinion would be fruitful.

Thanks!

Does "levels" in Q3. only means "high levels"? The paragraph says the number of diamonds depends on the level of the calcium and chrome irrespective of high or low.