Dr. Byrnes' TOEFL Reading Self-study Course: Sample Lecture
- This official TOEFL passage on minerals is packed with challenging questions.
- The Chinese website answer for Question 9 is incorrect.
Physical Properties of Minerals
Question 1(hard)
According to the paragraph, which of the following is a mistaken belief that people have about crystals?
A. Crystals always have a well-formed shape
B. Minerals are generally composed of crystals.
C. The atoms of a crystal have an orderly arrangement.
D. Crystals are always solid and inorganic.
Analysis
The mistaken belief = crystals are rare when in fact crystals are very common.
The reason for the mistake = most crystals do not exhibit their crystal form
So,
The mistaken belief = All crystals exhibit their crystal form
According to the passage, things are crystal even if they do not exhibit the external form that reflects the internal order. But people think that something is a crystal only if it exhibits the external form that reflects the internal order.
A is the mistaken belief people have. “Always” is an absolute term, which can make the idea expressed with it false. Mistakes are usually related to believing something in absolute terms.
B is a true fact.
C is a true fact.
D is false. What is always solid and inorganic is mineral.
Answer: A
Question 2 (hard)
Why is the color of a mineral an "an unreliable diagnostic property"?
Different minerals can have the same color
The color is often not a result of the chemical makeup that determines the identity of the mineral.
The color of a mineral cannot be predicted from knowing what foreign ions it contains.
No two pieces of the same mineral have exactly the same color.
Analysis
“Unreliable” suggests that the method works sometimes and does not work some other times. Color is an unreliable diagnostic property because the same minerals can have different colors due to the inclusion of impurities. But it also says that sulfur and malachite do have inherent coloration because their color is a consequence of their chemical makeup and do not vary much.
A is not the reason that the color of a mineral is an unreliable diagnostic property. A is a trap.
B: color can be due to the inclusion of impurities, instead of what? According to the passage, sulfur and malachite do have inherent coloration because their colors are consequences of their chemical makeup. So we can infer that the color of a mineral can be due to the inclusion of impurities, instead of the consequence of its own chemical makeup. So B is correct.
C misses the point
D is wrong. “No” is an absolute word, and sulfur and malachite are counterexamples.
Answer: B
Question 3 (very easy)
According to the paragraph, how do different samples of the same mineral come to exhibit a variety of colors?
A. The samples have different crystalline structures.
B. The samples contain different varieties of quartz.
C. The samples differ in the impurities they contain
D. The samples were formed in different exotic conditions.
Analysis
This is practically the same question as the previous question, but is much easier.
Answer: C
Question 4 (medium)
Which of the following can be inferred about streak from the paragraph?
When a sample of a mineral is rubbed on unglazed porcelain, the color of the streak is usually the same as the color of the sample.
In most cases, different samples of a mineral produce streaks that are all of the same color even though the samples themselves are of different colors.
When a streak is made, the impurities in the mineral are removed and the true color of the mineral is revealed
Streak color is reliable for identifying minerals because a given mineral sample always yields the same color of streak each time it is rubbed
Analysis
So, we can infer that, even though the color of a mineral varies from sample to sample, their streaks remain the same.
A is a trap. The color of the streak can be different from the color of the sample.
B is true.
C is not mentioned.
D is kind of relevant but not exactly since D is not the point made in the passage. More importantly, “always” makes the claim made in D questionable.
Answer: B
Question 5 (hard)
The discussion of Mohs' scale in the paragraph answers which of the following questions?
A. How was it determined that Mohs' scale would have ten minerals?
B. Is quartz one of the ten minerals that determine Mohs' scale?
C. Does Mohs' scale apply to materials other than minerals?
D. What mineral is harder than quartz and softer than diamond?
Analysis
A is not mentioned.
B can be tricky if you are a geologist. It is true that quartz is one of Mohs’ ten minerals, but the passage does not mention this. So, we cannot know whether quartz is one of the Mohs’ 10 minerals.
C: A fingernail, copper penny, and a piece of glass are not minerals since they are man-made or organic. So C can be answered.
D: We cannot know D since no information on this is provided.
Answer: C
Question 6 (easy)
It can be inferred from the paragraph that the mineral quartz
A. has no fixed degree of hardness
B. might scratch the surface of a diamond
C. is harder than calcite
D. has atoms that are weakly bonded to each other
Analysis
According to the passage, “the mineral calcite, which has a hardness of three, will scratch your fingernail but will not scratch glass Quartz” So, C is right.
Answer: C
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Question 7 (easy)
According to the paragraph, which of the following is true of the cleavage of micas?
A. Micas are the only minerals to break along planes of weak bonding
B. Micas exhibit poor cleavage because they tend to break unevenly.
C. Micas break in one direction, forming thin sheets with smooth surfaces
D. Micas break in several directions, forming a number of angles and planes.
Analysis
According to the passage, “The simplest type of cleavage is exhibited by the micas. Because the micas have excellent cleavage in one direction, they break to form thin, flat sheets.”
Answer: C
Question 8 (medium)
According to the paragraph, minerals that exhibit no cleavage
A. break evenly in more than one direction
B. have no crystalline form
C. shatter in pieces of various shapes and sizes
D. have surfaces that resemble broken glass
Analysis
This is another simple question. According to the passage, minerals that exhibit no cleavage fracture, breaking into various forms.
Answer: C
Question 9 (hard)
Why does the author warn Cleavage should not be confused with crystal form?
A. Because most people have the mistaken belief that the surfaces of crystals are planes of crystal cleavage
B. Because the author's characterization of cleavage in terms of smooth planes and the angles between them could easily be mistaken for a description of crystal form
C. To make the point that crystal form and cleavage are the same property only in the simplest cases of cleavage, such as mica
D. To introduce a discussion of minerals the have cleavage but not crystal form
Analysis
A Chinese website says the answer is A, but A cannot be inferred since there is no mention or hint of “most people have the mistaken belief that the surfaces of crystals are planes of crystal cleavage.” B on the other hand can be supported since the professor mentions this after he explains cleavages in terms of smooth planes and the angles between them as follows: “When minerals break evenly in more than one direction, cleavage is described by the number of planes exhibited and the angles at which they meet. Cleavage should not be confused with crystal form.
Answer: B