Reference no: EM133097000

Exercise - Mineral and Rock Resources

Explore the connection between society and its use of mineral and rock resources. Of special interest will be how our use of these resources is dependent upon their physical and chemical properties.

Part I - Mineral Properties and Applications

Recall that a mineral is defined as a naturally occurring, inorganic solid composed of one or more elements in which the individual atoms are arranged in an orderly manner called a crystalline structure. As illustrated in Figure 10.1, atoms are assembled in a three-dimensional pattern that repeats itself throughout the structure.

Hardness
The physical property known as hardness is defined as the ability to resist scratching. When one substance is harder than another it means it can scratch or cut the softer substance. This process of material being removed by scratching is referred to as abrasion. A common example is when you rub up against something hard, such as concrete or carpeting, and some of your skin is removed. Clearly, our skin easily undergoes abrasion because it is quite soft compared
to most substances.

1) The mineral we call diamond is the hardest known substance on Earth. Explain why attaching small pieces of diamond to the tips of saw blades and drill bits makes the best type of tools for cutting through hard objects.

2) The graph in Figure 10.2 shows the absolute hardness of several minerals (y-axis) plotted against their relative hardness (x-axis) on a 1 to 10 scale called the Mohs scale. Notice the considerable difference in the absolute hardness of diamond and the next hardest mineral, corundum. Using the fact that diamond's absolute hardness is about 8,000 kg/mm2, calculate how many times harder diamond is than each of the following minerals:

corundum (Al2O3) - 1,800 kg/mm2

quartz (SiO2) - 750 kg/mm2 calcite (CaCO3) - 135 kg/mm2 gypsum (CaSO4 2H2O) - 32 kg/mm2

3) Explain why small bits of corundum (Al2O3) would be used instead of diamond for making sandpaper to polish hardened steel, whose relative hardness is around 7.

4) Finely-ground calcite is often used to make household cleaners advertized as being mildly abrasive. Explain why calcite-based cleaners would be best for cleaning plastic materials, whose relative hardness is usually in the range of 3 to 4.

5) Gypsum is a very soft mineral (Figure 10.2) and the main component in drywall (also called sheetrock and wallboard). Drywall is used extensively in the interior of modern homes and businesses. During construction, sheets of drywall are normally cut into smaller pieces and then nailed to a building's wood or metal framing to form walls and ceilings. Explain how gypsum's softness makes it ideal for this type of application.

6) Figure 10.4 illustrates how the crystalline structure of graphite contains sheets of carbon atoms held together by strong chemical bonds. Between the individual sheets, however, are very weak bonds. This allows graphite to break quite easily, which is why it is one of the softest minerals. Humans have learned how to utilize graphite's softness by grinding the mineral into a powder and mixing it with a little clay to make pencils-erroneously called "lead" pencils as they do not contain lead. Describe what you think happens on an atomic scale when you push a pencil across a piece of paper such that it leaves a thin trace of graphite.

7) Unlike graphite, the mineral known as chert or flint (SiO2) is quite hard and will produce irregular fracture surfaces (Figure 10.3b). In freshly broken chert, the edge along where two fracture surfaces meet can be extremely sharp. Describe how ancient humans made use of chert's hardness and ability to form fracture surfaces.

Density
The density of a substance is defined as its mass divided by its volume. A baseball for example is denser than a Nerf ball because it has more mass packed into roughly the same volume. As with the properties of hardness and cleavage, humans have developed practical applications for certain minerals based on their density. One application where mineral density is important is the familiar hand tool we call a hammer. Here a heavy object is attached to a
wooden shaft and used to transfer kinetic energy to another object. Hammers are excellent tools for crushing, splitting, or shaping objects and for driving nails. For thousands of years people used rounded stones to make hammers because they were readily available in river beds. Once
humans learned how to extract metallic iron by heating iron-oxide minerals (e.g., Fe2O3) in a hot fire, iron hammers eventually replaced those made of stone.

8a) Suppose you made a hammer from a rounded stone whose volume was 500 cm3 (size of a half-liter bottle). Assuming crustal rocks have an average density of 2.8 g/cm3, calculate the mass of this stone in kilograms (kg). Be sure to show your math, including the units.

b) Calculate the kinetic energy in joules (kg-m2/s2) that you could transfer to another object if you were to swing the stone hammer with a velocity of 5 m/s.

9a) This time you make 500 cm3 hammer out of iron, whose density is 7.9 g/cm3. Determine the mass of iron in kilograms (kg). Be sure to show your math, including the units.

b) If you were to swing your iron hammer with the same velocity of 5 m/s, calculate the kinetic energy in joules (kg-m2/s2) you could transfer to another object.

10) Suppose that a prehistoric person was able to switch from a stone to an iron hammer.
Describe what the energy difference between the hammers would mean, in practical terms, to the user.

Part II - Consumption of Mineral Resources

From Table 10.1 you can see that each American is responsible for using over 20,000 lbs (10 tons) of stone, sand, and gravel on a per-capita basis each year. These basic rock materials account for 87% of all U.S. mineral consumption. Coming in a distant second is cement, where per-capita consumption is 841 lbs, or 3.5% of all U.S. mineral consumption. The other major non-metallic resources are salt, phosphate rock, and clays. With respect to metals, iron is clearly the most widely used. Although the use of aluminum, copper, lead, zinc, and gold is relatively small in terms of weight, these metals nonetheless have very important applications in society. In this section we will examine some of the ways in which society uses both non- metallic and metallic mineral resources.

Basic Rock Resources

11) At 20,000 lbs (10 tons) per year, stone, sand, and gravel resources represent the vast majority of U.S. mineral consumption. However, no one personally uses 10 tons of these basic rock materials around their home each year. Explain then where most of this rock material is likely being used.

12) There are limited reserves that can currently be mined economically for many of the mineral resources listed in Table 10.1. Do you think that the reserves of stone, sand, and gravel are also limited? Explain why or why not.

13a) Based on the chemical formulas of calcite (CaCO3) and lime (CaO), what common compound do you suspect is released into the atmosphere when crushed limestone (calcite) is heated and converted into lime?

b) Explain how the production of cement products is contributing to the problem of global warming.

14) Because natural rainwater is slightly acidic, it slowly dissolves concrete as well as monuments composed of calcite (limestone and marble). In many areas, the acidity of rainfall has greatly increased due to the release of sulfur dioxide (SO2) gas that forms when sulfur- rich minerals in coal undergo combustion. What do you suspect this so-called "acid rain" is doing to our concrete highways and bridges?

15a) It is often stated that when the environmental costs associated with the mining and burning of coal are considered, coal is no longer the cheapest means of producing electricity. Explain who pays for the coal-related deterioration of society's highways and bridges.

b) What do you think would happen if the costs associated with replacing our concrete infrastructure were included in the price of coal, making coal-generated electricity more expensive?

Metallic Minerals
Humans have discovered many important applications for the metals listed in Table 10.2.
For example, because iron (Fe) is strong and quite abundant, it is used to make large quantities of structural steel. Although aluminum (Al) is not as strong as iron, its lower density makes it ideal in applications where weight is a critical factor, such as airplanes and fuel-efficient vehicles. Another extremely useful property of metals is their ability to conduct electricity. For example, copper (Cu) is used in the wiring that carries electricity throughout our homes and cars. It is also used in the circuits of countless electronic devices, including cell phones, computers, and televisions. The modern society we have come to know would simply not exist were it not for the unique properties of metals.

16) Since silver (Ag) is a better electrical conductor than copper, provide an explanation as to why copper is used rather than silver in most applications. Hint, see Table 10.2.

17) The photo in Figure 10.5a shows a standard copper wire for carrying electricity to outlets and switches in our homes and businesses. In addition to being a good electrical conductor, copper is also highly ductile, which means it tends not to break when drawn out or stretched. Explain why being ductile is important when it comes to electrical wiring. Hint: examine photo (A) below.

18) Notice that the wire in Figure 10.5b actually consists of several fine strands of insulated copper wire. If the function of the wire in photo (A) is to supply electricity throughout a building, what do you suppose is the purpose of the bundled set of insulated wires in (B)?

19) From Table 10.3 you can see that the overall U.S. recycling rate of major metals is about 48%. Compare this to 28% U.S. recycling rate for glass and plastics. Provide one or more reasons why metals are far more likely to be recycled in the U.S. than glass and plastics.

Attachment:- Mineral and Rock Resources.rar