昆明理工大学复试原题-英语(共2页)

1、精选优质文档-倾情为你奉上2. The Outer Part of the Earths Crust Bedrock is the solid rock that is exposed at the surface or immediately underlies soil and loose surface debris. Regolith is relatively thin covering of soil and unconsolidated rock waste that hides the bedrock in most areas. Bedrock is continuous a

2、nd may consist of any kind of rock, whereas regolith is discontinuous, although generally present. Regolith tends to be a few tens of feet thick or less, but may be much thicker. It may develop in place by the decay and disintegration of bedrock or consist of transported materials. Soil refers to th

3、e upper portion of the regolith which has been so altered by physical, chemical, and biological processes that it can support rooted vegetation. However, soil may be absent from an area. By direct observation, man has access to only a very thin outer part of the crust, the deepest mines penetrate le

4、ss than 2 miles (3 km) beneath the surface, and the deepest wells about 5 miles (8 km). However, certain rocks now exposed at the surface may once have been buried several miles below it. Chemical analyses have been made for rocks of various types, and the proportions of the elements in the outer 10

5、-mile (16 km) zone of the lithosphere have been estimated. Eight elements apparently constitute more than 98% by weight of this zone: oxygen (most abundant), silicon, aluminium, iron, calcium, sodium, potassium, and magnesium (least abundant). The following mnemonic expression arranges. These eight

6、elements in the order of their relative abundances: “Only Silly Artists In College Study past Midnight”. If the materials in the atmosphere and hydrosphere are added to those of the 10-mile zone, percentages are changed only slightly. Of these eight elements oxygen and silicon combined as silica(SiO

7、2) make up about three-fourths of the total. Thus the silicate minerals are the most abundant in the crust, especially the feldspars, pyroxenes, amphiboles, micas, and quartz.4. Weathering and Soils The principal significance of the different climatic types to the student of geology lies in their in

8、fluence on soil formation and on erosion. Each climatic environment places its own stamp upon the soils developed there, and each influences, through its control over vegetation, amount of rainfall, and evaporation losses, the geological processes involved in molding the details of the earths surfac

9、e. Erosion, the process of removal of rock waste, will be discussed in later chapters, here, we will examine the influence of several different climatic environments upon the weathering of different rock types.The most familiar example of weathering is the etching and discoloration of the surface of

10、 an unpainted board left out-of-doors. Rock, exposed on the earths surface, also decays and leaches, but much more slowly. If the product of rock decay is merely broken and discolored, it is called mantle rock, but if it is loose and porous enough for plants to find a foothold, it is called soil.Soi

11、l is more common than rock at the earths surface. Almost all outcrops of rock are less firm-more easily crumbled and broken-than is the same rock at a depth of 20 or 100 feet. Many rocks that are black or steel gray where penetrated in mines, wells, or deep quarries are yellow or brown in outcrops.

12、In some, the yellow color is a mere stain on or near cracks, but in others it is more pervasive and is accompanied by drastic changes in mineral composition of the rock. That the changes result from weathering is shown by observations on building stones. For example, the exposed faces of the sandsto

13、ne used in the older buildings at Stamford University turned yellow in 5 to 10 years, and, where exposed to repeated wettings, began to crumble in 20 to 30 years.5. MineralsMost minerals are chemical compounds; that is, they consist of two or more elements in combination. Of course there are excepti

14、ons, such as gold, copper, sulphur, and carbon, which may occur as elements by themselves as well as in chemical compounds. Minerals are naturally occurring substances. This statement rules out laboratory creations. Minerals have a reasonably definite chemical composition. Since they are naturally o

15、ccurring substances, and not laboratory products, only rarely are they chemically pure compounds. For this reason, such properties as color may vary over a range as wide as from black to white, depending on the percentage of elements present for any mineral. Minerals also have certain physical prope

16、rties, determined by their chemical composition and by the geometric arrangement of the atoms composing them. It is this atomic arrangement that determines the crystal form of a mineral. Other properties include such things as color, hardness, and specific gravity.In summary, then, a mineral may be

17、defined as (1) a naturally occurring substance with (2) a fairly definite chemical composition and (3) characteristic physical properties by which it may be identified. In short, a typical mineral is a crystalline solid and is an inorganic substance. Most are chemical compounds, but a few, such as t

18、he diamond, may consist of a single element.Before we discuss the characteristics of individual minerals we should learn of the essential properties which are the chief means of their identification. Physical properties are the things we can see, or feel, or, for such minerals as halite (rock salt), taste. True enough, the chemical composition is possibly the most diagnostic property a mineral possesses, but few of us are going to pack along a fully equipped chemical laboratory to be used for mineral identification on a field trip. Since one of the critical differences between minerals and