Amineralis a naturally occurringsolidformed by inorganic processes. Since theinternalstructure and chemicalcompositionof amineralare difficult todeterminewithout the aid ofsophisticatedtests andapparatus, the more easily recognizedphysicalproperties are used inidentification.

Most people think of acrystalas ararecommodity, when in fact most inorganicsolidobjects are composed of crystals. Thereasonfor this misconception is that most crystals do notexhibittheircrystalform: theexternalform of amineralthat reflects the orderlyinternalarrangement of its atoms. Whenever amineralforms withoutspacerestrictions,individualcrystals with well-formedcrystalfaces will develop. Some crystals, such as those of themineralquartz, have a verydistinctivecrystalform that can be helpful inidentification. However, most of the time,crystalgrowth is interrupted because of competition forspace, resulting in an intergrownmassof crystals, none of which exhibitscrystalform.

Although color is anobviousfeature of amineral, it is often an unreliablediagnosticproperty. Slightimpurities in thecommonmineralquartz, for example, give it avarietyof colors, including pink,purple(amethyst), white, andevenblack. When amineral, such asquartz, exhibits avarietyof colors, it is said topossessexoticcoloration. Exoticcolorationis usually caused by theinclusionof impurities, such as foreign ions, in thecrystallinestructure. Other minerals — for example,sulfur, which is yellow, and malachite, which is bright green — are said to haveinherentcolorationbecause their color is aconsequenceof their chemical makeup and does notvarysignificantly.

Streak is the color of amineralin its powdered form and is obtained by rubbing amineralacrossaplateof unglazedporcelain. Whereas the color of amineraloften varies fromsampletosample, the streak usually does not and isthereforethe morereliableproperty.

Lusteris theappearanceorqualityof light reflected from the surface of amineral. Minerals that have theappearanceof metals,regardlessof color, are said to have ametallicluster. Minerals with a nonmetalliclusterare described by various adjectives, including vitreous (glassy) pearly, silky, resinous, and earthy (dull).

One of the most usefuldiagnosticproperties of amineralis hardness, theresistanceof amineraltoabrasionor scratching. Thispropertyisdeterminedby rubbing amineralof unknown hardness against one of known hardness, or vice versa. A numerical value can be obtained by using Mohs'scaleof hardness, which consists of ten minerals arranged in order from talc, the softest, at number one, to diamond, the hardest, at number ten. Anymineralof unknown hardness can be compared with these or with other objects of known hardness. For example, a fingernail has a hardness of 2.5, acopperpenny 5, and a piece of glass 5.5. Themineralgypsum, which has a hardness of two, can be easily scratched with your fingernail. On the other hand, themineralcalcite which has a hardness of three, willscratchyour fingernail but will notscratchglass. Quartz, the hardest of thecommonminerals, willscratcha glassplate.

Thetendencyof amineraltobreakalongplanes of weak bonding is called cleavage. Minerals thatpossesscleavage are identified by the smooth, flat surfaces produced when themineralis broken. The simplest type of cleavage is exhibited by the micas. Because the micas have excellent cleavage in one direction, theybreakto form thin, flat sheets. Some minerals have several cleavage planes, which produce smooth surfaces when broken, while othersexhibitpoor cleavage, and still othersexhibitno cleavage at all. When mineralsbreakevenly in more than one direction, cleavage is described by the number of planes exhibited and the angles at which they meet. Cleavage should not beconfusedwithcrystalform. When amineralexhibits cleavage, it willbreakinto pieces that have the sameconfigurationas theoriginalsampledoes. Bycontrast,quartzcrystals do not have cleavage, and if broken, wouldshatterinto shapes that do notresembleeach other or theoriginalcrystals. Minerals that do notexhibitcleavage are said tofracturewhen broken. Somebreakinto pieces with smooth curved surfaces resembling broken glass. Othersbreakinto splinters or fibers, but mostfractureirregularly.

Questions:
question_stem: The word "apparatus" in the passage is closest in meaning to
choices: tag: A
text: equipment

tag: B
text: procedures

tag: C
text: experiments

tag: D
text: laboratories
answer_key: A
explanation: 答案 A。apparatus：n. 装置，设备；仪器；器官

question_stem: According to paragraph 2, which of the following is a mistaken belief that people have about crystals?
choices: tag: A
text: Crystals always have a well-formed shape.

tag: B
text: Minerals are generally composed of crystals.

tag: C
text: The atoms of a crystal have an orderly arrangement.

tag: D
text: Crystals are always solid and inorganic.
answer_key: A
explanation: 答案 A。根据题干信息 mistaken belief、crystals 定位到第1、2句，第1句提出错误的看法，第2句话解释产生错误看法的原因，即大部分人觉得 crystal is rare，因为 most crystals do not exhibit their crystal form。但是选项里面没有一个是符合的，故而需要接着往后理解，第3句话开始主要讨论 crystal 的外形，没有 space restrictions，crystal 是 well-formed crystal faces，但是大部分时候，因为收到空间竞争，所以 crystal do not exhibit their crystal form。所以人们错误的看法觉得 crystal 少是因为他们看到的 well-formed crystal 少，故而答案选 A。

question_stem: According to paragraph 3, how do different samples of the same mineral come to exhibit a variety of colors?
choices: tag: A
text: The samples have different crystalline structures.

tag: B
text: The samples contain different varieties of quartz.

tag: C
text: The samples differ in the impurities they contain.

tag: D
text: The samples were formed in different exotic conditions.
answer_key: C
explanation: 答案 C。根据题干信息 different samples、a variety of colors 定位到第2句话 Slight impurities in the common mineral quartz, for example, give it a variety of colors, including pink, purple (amethyst), white, and even black，少许杂质使得矿物石英呈现各种颜色。所以答案选 C。

question_stem: Which of the following can be inferred about streak from paragraph 4?
choices: tag: A
text: 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.

tag: B
text: 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.

tag: C
text: When a streak is made. the impurities in the mineral are removed and the true color of the mineral is revealed.

tag: D
text: Streak color is reliable for identifying minerals because a given mineral sample always yields the same color of streak each time it is rubbed.
answer_key: B
explanation: 答案 B。整段讲述 streak，因此需要整段理解，两句话，第1句大意：streak 是粉末状矿物的颜色，以及获取的方法是 rubbing a mineral across a plate of unglazed porcelain；第2句大意：不同矿物样本的颜色不尽相同，但 streak 通常不会有区别，因此可靠性更高。选 B，对应第二句话，sample 不一样，但是 sample 磨成的 streak 颜色是一样的。A 混淆信息，sample 磨成 streak 之后，streak 之间的颜色是不变的，并不是与原先的 sample 一致；C 未提到 impurities；D 中的原因 a given mineral sample always yields the same color of streak each time it is rubbed 错了，不是一个 sample 的颜色每次 rub 的 streak 一致，而是同一个矿物质不同 sample 产生的 streaks 颜色不变。

question_stem: It can be inferred from paragraph 6 that the mineral quartz
choices: tag: A
text: has no fixed degree of hardness

tag: B
text: might scratch the surface of a diamond

tag: C
text: is harder than calcite

tag: D
text: has atoms that are weakly bonded to each other
answer_key: C
explanation: 答案 C。根据题干信息 mineral quartz 定位信息到最后一句话，句中出现了最高级比较 hardest，也可以参考就近句子，看看比较对象，前两句主要介绍了各种材料的硬度，最后一句讲到 Quartz, the hardest of the common minerals, will scratch a glass plate，也就是硬度大于5.5。所以答案选 C。

question_stem: The word "configuration" in the passage is closest in meaning to
choices: tag: A
text: effect

tag: B
text: range

tag: C
text: transformation

tag: D
text: form
answer_key: D
explanation: 答案 D。configuration：配置；结构；外形。

question_stem: According to paragraph 7, which of the following is true of the cleavage of micas?
choices: tag: A
text: Micas are the only minerals to break along planes of weak bonding.

tag: B
text: Micas exhibit poor cleavage because they tend to break unevenly.

tag: C
text: Micas break in one direction, forming thin sheets with smooth surfaces.

tag: D
text: Micas break in several directions, forming a number of angles and planes.
answer_key: C
explanation: 答案 C。题干信息 cleavage of micas 定位到第3、4句，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.故而答案选 C。

question_stem: Why does the author warn "Cleavage should not be confused with crystal form"?
choices: tag: A
text: Because most people have the mistaken belief that the surfaces of crystals are planes of crystal cleavage

tag: B
text: 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

tag: C
text: To make the point that crystal form and cleavage are the same property only in the simplest cases of cleavage, such as mica.

tag: D
text: To introduce a discussion of minerals the have cleavage but not crystal form
answer_key: B
explanation: 答案 B。定位题干句子之后，优先考虑上文就近两句，大意是分类介绍物质 cleavage 情况，有些矿物有多个 cleavage planes，碎裂时产生 smooth surfaces，其他的 poor cleavage, 还有其他的没有 cleavage。所以无法得出最直接的关系。再结合后文，When a mineral exhibits cleavage, it will break into pieces that have the same configuration as the original sample does，大意是矿物呈现 cleavage 时，会呈现出跟矿物原始样本一样的形态结构。也就是作者提到题干信息的目的是为了强调相同形态的 cleavage 和 crystal 之间本质是不同的，但很容易混淆。所以答案选 B。A 中的 the surfaces of crystals are planes of crystal cleavage 文章未提及；C 与原文意思相反了；D 中的 introduce a discussion minerals 这一点不符合，后文并未对有 cleavage 但没有 crystal form 的矿物进行讨论。