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Diamonds, an occasional component of rare igneous rocks call

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Diamonds, an occasional component of rare igneous rocks call [#permalink] New post 12 Jan 2019, 04:30
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92% (04:00) correct 7% (07:46) wrong based on 14 sessions
Diamonds, an occasional component of rare igneous rocks called lamproites and kimberlites, have never been dated satisfactorily. However, some diamonds contain minute inclusions of silicate minerals, commonly olivine, pyroxene, and garnet. These minerals can be dated by radioactive decay techniques because of the very small quantities of radioactive trace elements they, in turn, contain. Usually, it is possible to conclude that the inclusions are older than their diamond hosts, but with little indication of the time interval involved. Sometimes, however, the crystal form of the silicate inclusions is observed to resemble more closely the internal structure of diamond than that of other silicate minerals. It is not known how rare this resemblance is, or whether it is most often seen in inclusions of silicates such as garnet, whose crystallography is generally somewhat similar to that of diamond; but when present, the resemblance is regarded as compelling evidence that the diamonds and inclusions are truly cogenetic.
17. The author implies that silicate inclusions were most often formed

(A) with small diamonds inside of them
(B) with trace elements derived from their host minerals
(C) by the radioactive decay of rare igneous rocks
(D) at an earlier period than were their host minerals
(E) from the crystallization of rare igneous material

[Reveal] Spoiler: OA
D


18. According to the passage, the age of silicate minerals included in diamonds can be determined due to a feature of the

(A) trace elements in the diamond hosts
(B) trace elements in the rock surrounding the diamonds
(C) trace elements in the silicate minerals
(D) silicate minerals' crystal structure
(E) host diamonds' crystal structure

[Reveal] Spoiler: OA
C


19. The author states that which of the following generally has a crystal structure similar to that of diamond?

(A) Lamproite
(B) Kimberlite
(C) Olivine
(D) Pyroxene
(E) Garnet

[Reveal] Spoiler: OA
E


20. The main purpose of the passage is to

(A) explain why it has not been possible to determine the age of diamonds
(B) explain how it might be possible to date some diamonds
(C) compare two alternative approaches to determining the age of diamonds
(D) compare a method of dating diamonds with a method used to date certain silicate minerals
(E) compare the age of diamonds with that of certain silicate minerals contained within them

[Reveal] Spoiler: OA
B


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Re: Diamonds, an occasional component of rare igneous rocks call [#permalink] New post 12 Jan 2019, 21:25

+1 kudos to the posts containing answer explanations of all questions

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Re: Diamonds, an occasional component of rare igneous rocks call [#permalink] New post 08 Mar 2019, 22:55
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2 mins 58 secs... all correct. Great short passage @carcass, as usual, your passages are a treat to solve :-) Kind of felt similar to the movie Inception :-)

Diamonds have never been dated satisfactorily, however, some diamonds contain minute inclusions of silicate minerals - which can be dated fairly accurate due to radioactive decay of minute radioactive materials within those minerals. The passage goes on to mention that most silicate mineral impurities are older than the diamonds but a particular type "Garnet" has a structure very similar to the diamond and cab thought of as cogenetic.


The author implies that silicate inclusions were most often formed
(A) with small diamonds inside of them Opposite is true - some diamonds have silicate material inside them
(B) with trace elements derived from their host minerals nonsensical, discard.
(C) by the radioactive decay of rare igneous rocks Again, the two things are not related
(D) at an earlier period than were their host minerals Perfect - this is verbatim from the passage
(E) from the crystallization of rare igneous material not mentioned anywhere in the passage

Easy detail question, literally doable in under 10 secs :-)
According to the passage, the age of silicate minerals included in diamonds can be determined due to a feature of the
(A) trace elements in the diamond hosts Not there yet
(B) trace elements in the rock surrounding the diamonds Out of scope, rock surrounding diamonds what?
(C) trace elements in the silicate minerals Bingo - the characteristic being talked about is radioactivity and trace radioactive elements are present inside the silicate crystals which are inside the diamonds which are inside the igneous rocks! Kind of feels like the movie inception :-D
(D) silicate minerals' crystal structure not related to crystal structure
(E) host diamonds' crystal structure discard for same as above

It doesn't get easier than this ;-)
The author states that which of the following generally has a crystal structure similar to that of diamond?
(A) Lamproite
(B) Kimberlite
(C) Olivine
(D) Pyroxene
(E) Garnet Tick

Finally a challenging question - we need to realize that the main point of the passage is revealed right at the start - "now some diamonds can be dated accurately" is the main point
The main purpose of the passage is to
(A) explain why it has not been possible to determine the age of diamonds TRAP - a play of words - the author does not want to dwell too much on the past but has made a passing reference
(B) explain how it might be possible to date some diamonds Perfect - this is the reason why the author has written the passage
(C) compare two alternative approaches to determining the age of diamonds No two methods given
(D) compare a method of dating diamonds with a method used to date certain silicate minerals Again - flawed for same reason as above
(E) compare the age of diamonds with that of certain silicate minerals contained within them We are not comparing anything!

Hope my answers are helpful. :-)
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Re: Diamonds, an occasional component of rare igneous rocks call [#permalink] New post 23 Mar 2019, 04:57
What does a "cogenetic" mean? I have not found definition yet.
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Re: Diamonds, an occasional component of rare igneous rocks call [#permalink] New post 23 Mar 2019, 05:33
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https://glosbe.com/en/en/cogenetic

Created at the same time and place as another

Think about genes. They, actually, forge what we really are as a species.

We are made of genes, so they create us , somehow.

Co = together = cogenetic.

Hope this helps.

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Re: Diamonds, an occasional component of rare igneous rocks call [#permalink] New post 23 Mar 2019, 05:48
Thanks!
Re: Diamonds, an occasional component of rare igneous rocks call   [#permalink] 23 Mar 2019, 05:48
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