FragileSystems.pdf

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Department
Earth and Ocean Sciences
Course
EOSC 114
Professor
All Professors
Semester
Spring

Description
A Fragile System? OVERVIEW Natural cataclysmic events affect the Earth every day, and are a normal part of the Earth-ocean-atmosphere system. However, these same events (landslides, earthquakes, hurricanes, tsunami, etc.) can kill people or reduce the quality of life. This dichotomy motivates the title for this Module: Is the Earth a fragile system? To address this question, you start by reviewing the metrics used to describe our world. You next look at the materials that make up the Earth, ocean, and atmosphere. Natural processes can be disasters because of their tremendous energy release, so you will review the types of energy. Some disasters such as earthquakes and tsunami propagate as waves, which you will study. With this background, you will examine the relationship between population growth and the societal impact of natural disasters, and make your own decisions about whether the Earth is a fragile system. INSTRUCTIONS and QUIZ Study and make notes based on the following Course Notes and the textbook reading assignments. The Learning Goals will allow you to assess your understanding of the key concepts. This Module will be covered in the Fragile Systems (FS) Quiz. Consult the FAQs for information on taking the Quizzes. LEARNING GOALS The goal of this Module is to prepare you for the Modules that follow; namely, to help you understand the basic concepts used to describe different disasters, and to help you put disasters into perspective. Use the following learning goals as a self-assessment tool to help you gauge your understanding of the course material presented in this Module. After you complete this Module you will be able to: A. Explain what density is and how it relates to stratification. B. Explain why disaster scales are based on the Order-of-Magnitude concept and interpret graphs with logarithmic scales. C. Relate natural-disaster risk and intensity to frequency, return period, and consequences (costs). D. Explain how recent disasters were associated with the concentration or dilution of energy. E. Get the disaster info you need from reliable sources. F. List the 1st and 2nd most common elements in the Earth, ocean, and atmosphere. G. Describe how viscosity and compressibility relate to the phase of matter. H. Be able to diagnose the type of strain by the way a material deforms. I. Explain why gravity affects motion and energy. J. List the 5 types of energy, and describe what causes them to vary. K. Explain (with examples) how energy conservation applies to natural disasters. 1 of 42 L. Describe relationships between force, pressure, stress, strain, energy, and power. M. Describe population growth and explain why it is important for natural disasters. N. Explain how Earth's carrying capacity and overpopulation are related to the fate of the human race, and anticipate your role in it. ORGANIZATION A Fragile System? contains five Lessons (1 - 5) that span the learning goals listed above. LESSON TOPIC 1 Natural Disasters are Rare Events 2 Materials 3 Energy 4 Waves and Turbulence 5 Is the Earth a Fragile System? READINGS: A Fragile System? Read all of Chapter 1. A Global and Canadian Outlook on Natural Disasters Read all of Chapter 2. Energy Flows Important Notes: a) Don't memorize any Tables but understand the main points that the Tables illustrate. b) Figures contain very important information, too! Read the captions and understand the ideas being illustrated Lesson 1: Natural Disasters are Rare Events OUTLINE Recall that the goal of this Module is to prepare you for the Modules that follow; namely, to help you understand the basic concepts used to describe different disasters, and to help you put disasters into perspective. So lets jump right in and review some of the metrics used to measure our world, and how to quantify the intensity of disasters and their frequency of occurrence. A. SI magnitude prefixes B. Time measures C. Distance (space) measures D. Mass (matter) measures E. Density F. Stratification G. Quantifying Rare Events H. Disaster Scales I. Intensity vs. Frequency A. Magnitude Prefixes The International System of Units (SI) specifies the following prefixes to represent various multiples or magnitudes: 3 k = kilo = thousand = 1,000 = 1 x 10 M = mega = million = 1,000,000 6 = 1 x 10 2 of 42 G = giga = billion = 1,000,000,000 = 1 x 109 T = tera = trillion = 1,000,000,000,000 = 1 x 1012 c = centi = hundredth = 0.01 = 1 x 10-2 m = milli = thousandth = 0.001 = 1 x 10-3 µ = micro = millionth = 0.000001 = 1 x 10-6 -9 n = nano = billionth = 0.000000001 = 1 x 10 FAMILIAR EXAMPLES INCLUDE: 1 kilometre = a thousand metres 1 gigabyte = a billion bytes To learn more about prefixes and SI units, see http://en.wikipedia.org/wiki/SI B. Time The SI standard for time is the second (s). Other non-SI time units (but accepted for use with SI) derived from this standard include: 1 minute (min) = 60 s 1 hour (h) = 60 min 1 day (d) = 24 h We also frequently use other time units that are not standard (i.e., can vary): 1 year (yr) = 365.25 d (approximately; consider year and leap years.) (Note: often we use the word annum with its abbreviation (a) in place of year.) 1 millennium = 1000 yr = 1000 a We can use these time units and prefixes to describe some important events in the Earth's evolution: Age of Earth = 4.57 billion years = 4.57 Ga Age of oceans = 4.3 Ga Age of present ocean basins = 200 million years = 200 Ma (when supercontinent Pangaea broke-up into the present-day continents) Time before present when life begins = 3.8 Ga Time can also be used to quantify how many disasters involve a sudden release of large amounts of energy, even though the energy supply is initially very slow. Thus the energy must first be concentrated, but this takes time. In the examples in the table below, the build- up time is greater than the release time. Table FS.1 Time scale of build up and release of energy during natural disasters DISASTER BUILD-UP RELEASE Earthquakes years minutes Volcanoes decades days Hurricanes months days Thunderstorms hours minutes 3 of 42 Rogue waves hours seconds Landslides days seconds Meteor Impact millennia seconds Some of the disasters above inject so much energy in a short time, that subsequent events are triggered over longer times that can still be devastating. Namely, even after spreading or dilution of the initial energy release, the effects can still threaten lives and property: Table FS.2 Timescale of build up and release of energy during disaster events INITIAL CAUSE DISASTER BUILD-UP RELEASE Earthquake Tsunami minutes hours Thunderstorm Floods hours days Namely, for these cases the build-up time is less than the release time. Later in the course, we will study some other disasters such as: Storm surges Lahars After you study these, think about the relevant time scales. C. Space or Distance The SI standard unit of distance is the metre (m). Although there are no derived units with special names, we commonly use metres prefixed with a magnitude: 1 micrometre = 1 µm = 1 m / 1 million = 10–6 m 1 millimetre = 1 mm = 1 m / 1 thousand = 10–3 m 1 kilometre = 1 km = 1,000 m = 103 m We can use distance units to describe some typical scales of features on Earth: Earth radius: 6357 km Atmospheric thickness: The bottom portion (troposphere) that has the storms: 11 km To the top of the atmosphere (exosphere): 550 km Ocean depth: Average depth: 4 km Deepest portions, such as the Mariana Trench: 11 km Air molecule: 0.001 µm = 10m D. Mass Mass is what things are made of. It is matter. The SI standard unit of mass is the kilogram (kg). Derived units include: 4 of 42 1 gram (g) = 0.001 kg (this is the only SI unit where the prefix "kilo" is on the standard) A non-SI mass unit that is accepted for use with SI is: 1 tonne (t) = 1000 kg (also sometimes called a metric ton). A range of typical mass scales is illustrated by: mass of Earth: 5.97 × 1024 kg –26 mass of air molecule: 4.8 × 10 kg CAUTION: Sometimes in science, the same letter or symbol is used to abbreviate two or more different things (due to the limited number of letters and symbols available). For example, sometimes we let the variable called mass have the abbreviation "m". Other times, we use the abbreviation "m" to represent the unit of distance. This can be very confusing, and often can be resolved only from the context in which it is used. To help distinguish between variables and units, publishers often use italic fonts for variable names, and normal (roman) fonts for units. For example, the following equation, which we will study later in this course, has both variables and units: and could be confusing because "m" is used one place as a unit and another place as a variable. E. Density Density is defined as mass per unit volume. It describes how much mass fits into a space. To help visualize volume, recall that a cubic 3 metre (m ) is roughly the size of a large fish tank or a large cardboard box. This variable is sometimes given the symbol ρ or d. 3 –3 Its units are kg/m , which is sometimes written as kg-m . For comparison materials with different densities: density of iron = ρ 3 iron = 7870 kg / m density of ocean water = ρocean water = 1025 kg / m 3 density of air = ρair = 1.2 kg / m 3 CHECK YOUR UNDERSTANDING: A solid iron cannon ball will sink when immersed in a fluid. A) Yes B) No C) not enough info to answer F. Stratification 5 of 42 Density is important because less-dense materials float on top of denser materials, in the presence of gravity. For example, cream floats on milk. Oil floats on water. Steel floats on mercury. Fresh river water floats on top of salty ocean water. Continental crust (rocks that make up the continents) floats on top of oceanic crust (rocks that make up the sea floor). When more than two different materials are mixed together, the least dense floats to the top, the most dense sinks to the bottom, and the other materials form middle layers that are segregated such that density increases as you go downward. The end result is a layering of materials. Namely, the materials are stratified into layers. Over the long periods of geologic time, the materials that make up the earth have also become stratified. The most obvious is that the least dense (air) floats to the top, and the most dense (rocks) sinks to the bottom, leaving the middle-density materials (ocean) in the middle. But even within the atmosphere, the ocean, and the Earth, there is also stratification. The resulting layers are given names: 1. Atmosphere (listed from the top down) As shown in the figure on the left, the tops of each layer also have names, such as the tropopause at the top of the troposphere. Exosphere (where hydrogen and helium escape to space; NOT shown in Figure) Thermosphere Mesosphere Stratosphere Troposphere (the layer containing storms) Figure FS.1 The vertical temperature profile of the Earth's Atmosphere and its layers. 2. Ocean (listed from the top down) Surface zone / mixed layer Intermediate layer(s) Deep / abyssal / bottom layer 6 of 42 Figure FS.2 Stratification in the oceans is driven by changes in temperature and salinity, which determine seawater density. There are many other names for layers in the ocean. One series is based on the amount of light that reaches different layers (Figure on the left). The amount of available light determines the ecological layering. Sunlit zone Twilight zone Dark zone Abyss Trenches Figure FS.3 Ocean layers based on availability of light. and another based on their ecological characteristics (Figure on the right). Epipelagic zone Mesopelagic zone Bathypelagic zone Abyssopelagic zone Hadalpelagic zone 7 of 42 Figure FS.4 Ocean layers based on ecological parameters. 3. Earth (listed from the top down) Lithosphere (solid, crust) Asthenosphere (plastic rock) Mesosphere (solid rock) Outer core (liquid metal) Inner core (solid metal) Figure FS.5 Earth's internal layers based on chemicalandphysical characteristics. There are also other names for Earth layers as shown in Figure 2.6 of Abbott and Samson, 2012 (below): Crust Mantle Core 8 of 42 G. Quantifying Rare Events 1. Intensity. The phrase "order of magnitude" means something very specific in science. It means "power of ten". For example, if the number of students on the UBC-Vancouver campus is an order of magnitude greater than the number of students on the UBC- Okanagan campus, it means that the Vancouver campus has ten times as many students as at the Okanagan campus. Namely, if there are 4,000 students at the Okanagan campus, then there are 40,000 students at the Vancouver campus. We could also say that the Okanagan campus has an order of magnitude smaller enrollment than the Vancouver campus. Namely, it has one tenth the enrollment. Consider the following list of numbers: 10 = 1 10 1= 10 2 10 = 10 × 10 = 100 3 10 = 10 × 10 × 10 = 1,000 10 4= 10 × 10 × 10 × 10 = 10,000 We can generalize the above correlations as 10 P, where P is the power or exponent. Namely, P is a count of the number of zeros in the number. Aside: If you are afraid of common logarithms, don't be. The logarithm of 10 is just 1. The log of 100 is 2. Log(1000) = 3. ..and so forth. Namely, the log of a number is just a count of the number of zeros after the 1. Namely, P is just the logarithm of 10 . But what is the logarithm of any other number, such as 500. Well, we can guesstimate it fairly easily. 500 is between 100 and 1000. We already know that the log(100) = 2 , and the log(1000) = 3. Therefore, I would guess that the log(500) is somewhere between 2 and 3, let's guess 2.5. (When I use my calculator, I get log(500) = 2.7 , so I wasn't too far off.) Not too scary. 9 of 42 We can plot these numbers on a graph, as a function of P: This shape of curve, which starts rising very slowly at first for small values of P, but increases faster and faster as P gets larger, is called an exponential curve. But notice that much of the graph is off scale (too small, or too large). For P = 0, 1 and 2, the values ofare all plotted along the very bottom of this graph, so it is difficult to distinguish any differences. Also, for very large P such as P = 5, the curve is way off the top of the graph – again useless. 2. Intensity Using Logarithmic Scales. To avoid the graphic difficulty mentioned in the previous page, we can use a logarithmic graph, where the ordinate (the vertical axis of the graph) steps by powers of 10. Namely, the abscissa (horizontal axis) is linear, but the ordinate steps by orders of magnitude. See graph on left below: P This graph looks nice! Compare with the the graph on right presented previously. For each value of P, we can see the value of 10 from the graph. And we would have to extend this graph only a little along the ordinate to capture 10 . So why not use the power (to which 10 is raised) as a surrogate measure of the number? Namely, use power 3 as a surrogate measure for the number 1,000. Use power 4 as a surrogate for 10,000 and so forth. In fact, many disaster scales use just such a "power" surrogate to indicate intensity. For example, an earthquake of magnitude 6 is roughly an order of magnitude more violent than an earthquake of magnitude 5. Most disaster scales are this way. CHECK YOUR UNDERSTANDING: A disaster of intensity 6 is how much stronger than a disaster of intensity 4? (Assume these are order-of-magnitude scales.) A) 2 B) 10 C) 100 D) 10 4 10 of 42 6 E) 10 H. Disaster Scales Disaster scales are often named after the person who developed it. Here is a list of disaster scales for the disasters that we will study in this course. The details of each disaster scale will be explained in the other Modules of this course, when you learn about each type of disaster. 1. Earth Richter Scale (earthquakes) Modified Mercalli Scale (earthquakes) Moment Magnitude Scale (earthquakes) Volcano Explosivity Index (volcanoes) 2. Ocean Beaufort Scale (wind and waves) Saffir-Simpson Scale (hurricanes) 3. Atmosphere dBZ (radar echo intensity of precipitation) Enhanced Fujita Scale (tornadoes) Torro Scale (tornadoes) 4. Impacts from Space Torino Scale (meteor strikes) I. Intensity vs. Frequency 1. Examples. More-intense disasters occur less frequently. Namely, intense disasters are relatively rare. The following graphs are from actual data of disaster occurrence vs. intensity. They are plotted on both normal graphs (linear vs. linear) on the left, and semi-log graphs (power-of-ten ordinate vs. linear abscissa) on the right. 11 of 42 Thankfully, each graph indeed shows that more-intense disasters happen less frequently. One way to quantify how often a disaster has occurred in the past is the "Return Period". This will be discussed next. 2. Return Period (RP) is the average number of years between disaster events of the same magnitude (M). When you hear phrases such as "a 50-year storm", or "a 100-year flood", these refer to a storm of such intensity that its return period averages once every 50 years, or a flood of such intensity that it occurs once every 100 years on average. Calculate it by: For example, if we have been recording hurricane damage for the past 70 years in the USA, and if a hurricane of intensity 5 on the Saffir- Simpson Scale has happened only twice in that period, then: The above calculation means that intense hurricanes (of magnitude 5) strike the USA only once every 35 years, on average. Why does this matter? Below is a map that shows what wind speed (km/h) in a given location has a return period of 50 years. For example, near the Great Lakes, winds of 90 km/h or faster occur only once every 50 years. However, over the Queen Charlotte Islands of British Columbia, much stronger winds, that of 140 km/h or faster occur once every 50 years. Thus, if you design a house that won't blow down during your remaining lifetime, you would want it to be able to withstand winds of 140 km/h if you built it on the Queen Charlottes. However, if you build you house near the Great Lakes, you would need it to withstand only winds of about 90 km/h. 12 of 42 Figure FS.6 A map of Canada showing contours of wind speed (in km per hour) with 50-year Return Periods. Map from Environment Canada. You must be very careful when you interpret and utilize return-period data. First, they are average statistics of PAST weather, not certainties of what will happen in the FUTURE. Second, although winds of 140 km/h happened once every 50 years on average, the actual time period between any two events could have been less or more than 50 years. Third, even though you might live for another 50 years in the Queen Charlottes, it is possible for you to experience a 160 km/h wind. Even if 160 km/h winds might have a return period of say 75 years, that does not prevent it from happening during the 50 years that you live there. Lastly, all the caveats above ignore the additional possibility that the climate might change between the past measurements and your future period of interest. CHECK YOUR UNDERSTANDING: 1. For SW Canada, extremely destructive earthquakes have occurred as plotted above with magenta bars. Estimate the return period (in years)? A) 155 years B) 286 years C) 572 years D) 2000 years E) not enough info to answer 2. Predict the year of the next earthquake. A) THIS year 13 of 42 B) approximately in the year 2065 C) approximately in the year 2295 D) approximately in the year 2581 E) not enough info to answer Summary At this point, you should have a good understanding of metrics used to measure our world, and how to quantify the intensity of disasters and their frequency of occurrence. In particular, we covered: A. SI magnitude prefixes B. Time measures C. Distance (space) measures D. Mass (matter) measures E. Density F. Stratification G. Quantifying Rare Events H. Disaster Scales I. Intensity vs. Frequency The important points are that: We must use common metrics in order to share information efficiently In physical sciences, the metric "value" always includes numbers and units. These concepts will be used in all of the remaining Modules of this course, so feel free to refer back to this Lesson if you can't recall some of these basic information. The next Lesson will discuss the materials that make up our Earth, ocean, and atmosphere. Lesson 2: Materials OUTLINE Many disasters involve the movement or transport of, or change in, materials. For example, rocks break in earthquakes, water oscillates in tsunami, and air rises in thunderstorms. In this section, we examine the nature of materials. A. Elements and Atoms B. Key Elements Used in this Course C. Molecules and Ions D. Minerals E. Crystals F. Phases of Matter G. Properties of Materials A. Elements and Atoms Elements are the building blocks of our world. A chemical element consists of identical atoms. Thus, an atom is the smallest piece of an element. Atoms are made of protons, which have a (+) charge neutrons, which are neutral electrons, which have a (–) charge 14 of 42 Normally, the number of electrons and protons in an atom are equal, causing the atom to have no net charge (i.e., to be neutral). In modern physics, even these particles can be further subdivided. But we need not be concerned with such smaller subatomic particles for this course. Nucleus. The nucleus is the center of an atom. It holds the protons and neutrons. Swarming around the nucleus is the cloud of electrons. Atomic Number. Atoms (and the elements formed from them) are identified by the number of protons. This number is the atomic number. Atomic Mass Number. But because two or more versions of one element can have different numbers of neutrons, we define the atomic mass number to differentiate between these versions. The atomic mass number is the sum of:protons + neutrons = atomic mass number Isotopes. Isotopes are different versions of an element that have the same number of protons, but different numbers of neutrons. Namely, they have the same atomic number, but different atomic mass numbers. FOR EXAMPLE: We sometimes hear of "carbon dating" old materials. 12 The most abundant form of carbon (atomic number = 6) on Earth is carbon-12 or C; namely, it is the isotope of carbon having an atomic mass number of 12 (= 6 protons + 6 neutrons). It is a very stable isotope (luckily for us, because we humans are carbon- based life forms). 14 Carbon-14 or C is an isotope having an atomic mass number of 14 (= 6 protons + 8 neutrons). Carbon-14 is less prevalent on Earth, and is not stable; namely, it gradually decays with time. By comparing the relative amounts of 12C to 14C, and knowing the half-life (i.e., the 14 decay rate) of C, one can determine the age of the material. B. Key Elements used in this Course Elements are often listed in the periodic table. However, in this course, we are concerned with only a portion of known elements. Thus, instead of presenting the whole periodic table, we will list only the elements that are important for us. In Table FS.3 below, the first column refers to the name of each element. The next column shows the symbol or abbreviation used to represent the element. The last column gives a brief description of how these elements touch our lives. In this description, some elements are identified as being the (Gco) "greatest component of" a portion of the Earth/ocean/atmosphere system, while others are identified as being (Aco) "a component of" something. These descriptions, along with the element names and abbreviations, are important to remember. (You might be tested on which elements are the greatest, second greatest, etc. elements in a particular system.) Table FS.3 Key elements and their properties ELEMENT SYMBOL DESCRIPTION Hydrogen H Smallest atom; Aco water Helium He Non-reactive (noble gas); made by fusion in sun Aco most life forms on Earth; Aco coal, graphite, diamonds (yes, diamonds Carbon C burn; it is not true that "diamonds are forever") Nitrogen N Gco air; Aco nitric-acid rain Gco Earth's crust, 2nd Gco atmosphere; Aco water; very reactive, such as Oxygen O oxygen-based bleaches, and in combustion of the oxygen in air with other 15 of 42 flammable materials Sodium Na A very reactive metal; Aco salt in oceans Magnesium Mg A light metal; reactive; Aco the mineral called dolomite; Aco salt in oceans Aluminum Al A light metal used in cans, foil, aircraft; reactive; 3rd Gco Earth's crust Silicon Si A shiny silver-coloured semiconductor; 2nd Gco Earth's crust Phosphorus P Aco phosphate fertilizers Sulphur S Yellow; burnt match smell; Aco sulfuric-acid rain; Aco salt in oceans Chlorine Cl Very reactive (bleaches); Aco salt in oceans Argon Ar Argon is the third most common gas in the Earth's atmosphere Potassium K Very reactive metal; Aco salt in oceans Calcium Ca Aco limestone, bones, sea shells, salt in ocean A strong, light metal, often used in military aircraft and some computer Titanium Ti cases and eyeglass frames Manganese Mn A metal like iron A strong metal that is often combined with carbon to make steel; used in Iron Fe cars and in the steel beams and rebar of structures; Gco Earth's core; Aco meteorites; can become magnetic; 4th Gco Earth's crust Iridium Ir rare element, found in meteorites SURVEY QUESTION: Which single element do you feel you could NOT live without? A) Oxygen B) Carbon C) Hydrogen D) Silicon E) Other RECALL: Complete the summary table. A few cells have been filled to get you started. ABUNDANCE EARTH'S CORE EARTH'S CRUST OCEAN ATMOSPHERE Most abundant iron, Fe 2nd abundant hydrogen, H 3rd abundant (unknown) aluminum, Al argon, Ar C. Molecules and Ions Molecules. Atoms can combine to make molecules (compounds). The subscript in a chemical formula indicates number of atoms in a molecule. Normally, molecules have neutral overall charge (namely, the number of protons equals the number of electrons). Some molecules are held together by ionic bonds, where valences sum to zero. For this type of bond, one atom such as a metal loses one or more electrons (to leave itself positively charged) and gives them to another atom in the molecule (which becomes negatively charged). One common example is table salt, halite. 16 of 42 Other types of bonds are covalent bonds where electrons are shared between different atoms in a molecule. In the examples given in Table FS.4 below, the bonds between the atoms in a molecule are indicated with a single line for a single bond (–), a double line for two bonds (=), and a triple line for three bonds. Each bond represents one pair of electrons being shared. The superscripts indicate the valences (as listed earlier in the list of important elements), and the subscript tells how many of the atoms are grouped to form a molecule. Normally, the valences, when multiplied by the number of atoms, sums to zero in a molecule. Table FS.4 Selected compounds and their properties FORMULA NOTATION MOLECULE (ABBREVIATION) SHOWING BONDS Salt (halite) NaCl (ionic bond) Water H 2O H – O – H Carbon dioxide CO O = C = O 2 Diamonds C each C is bonded to four others Hydrogen gas H H – H 2 Nitrogen gas N 2 N {triple bond} N Oxygen gas O O = O 2 Ions (also known as Radicals). Tightly bonded groups of atoms that act as single units in molecules, but which are not complete molecules themselves because they carry a nonzero charge (sum of valences of all atoms). The net charge is indicated with the superscript. Table FS.5 Selected radicals and their properties RADICAL FORMULA RECIPE (ABBREVIATION) –2 +4 –2 Carbonate (CO3) 1 C + 3 O –2 +6 –2 Sulfate (SO 4 1 S + 4 O Silicate (SiO )4 +4 –2 4 1 Si + 4 O Hydroxyl (OH) –1 1 O –2 + 1 H1 FOR EXAMPLE: Seashells are made of the molecule "calcium carbonate". Namely, they have 1 calcium atom (which has a +2 valence) combined with a carbonate ion (the carbon and 3 atoms of oxygen, which taken together have a net valance of –2), yielding a molecule CaCO3with neutral charge. D. Minerals A mineral is naturally occurring solid element or molecule having a characteristic crystal structure and chemical composition. Some examples of minerals used in this course are: Table FS.6 Selected minerals and their properties 17 of 42 MINERAL CHEMICAL FORMULA IMAGE NAME NAME Silica (quartz)Silicon Dioxide SiO2 Calcite Calcium CaCO 3 (limestone) Carbonate Hematite Iron Oxide Fe2O 3 Magnetite Iron Oxide Fe3O 4 Pyrite (fools Iron Disulfide FeS gold) 2 E. Crystals Crystal Structures. When atoms in molecules line up in a regular lattice, the result is a crystal as shown in the images below. This alignment is caused by the various bonds. 18 of 42 Cleavage. Crystals often have directions of weakness through them, allowing the crystals to split along smooth planes. These cleavage planes follow the weakest bonds in the lattice. For example, the mineral mica easily separates along its cleavage planes into thin sheets of semi-transparent rock: Structural Failure. This is important for failure (fracture) of the material, such as in earthquakes. Selected Crystal Shapes. Table FS.7 Selected crystal shapes CRYSTAL SHAPE EXAMPLE IMAGE Cubic shaped line a box; has 6 sides halite (NaCl) galena (PbS) pyrite (FeS2 ) Note: in this photo, three separate cubic crystals grew together at an odd angle Octahedral shaped like two square pyramids stacked bottom to bottom; has 8 sides diamond (C) fluorite (CaF) 2 19 of 42 Hexagonal Column with Pyramid shaped like a pencil; namely, a 6- sided shaft capped on the end with a 6-sided pyramid quartz (SiO 2 ice (H2O) F. Phases of Matter The three phases of matter are solid, liquid, gas (vapour). One way to define them is by their physical characteristics of fluidity and compressibility. These will be defined in the next page. Solids: not very fluid not very compressible Liquids: very fluid not very compressible Gases: very fluid very compressible You might wonder why solids are defined as "not very fluid", instead of as "not fluid". The reason is that over geological time scales, some solids behave like fluids. FOR EXAMPLE: We consider ice as a solid form of water, but ice deforms and flows slowly in glaciers. Even some rocks can gradually deform and flow deep in the Earth, given enough pressure and a long enough period of time. Changes between phases have special names, most of which you will recognize: 20 of 42 CHECK YOUR UNDERSTANDING: If a material is very compressible and not very fluid, then you would classify it as a ______. A) gas B) liquid C) solid D) crystal E) none of the above G. Properties of Materials Compressibility is the ability of a material to be squeezed or expanded, so that the mass fills less or more space. Compression results in a change in density (mass / volume) of the object, because of the volume change. A material that is very compressible can be squeezed into a very small space. Fluidity is the ability of a material to flow; a material that is "very fluid" flows very easily. Fluids include: Liquids, for example, water Gases, for example, air; Yes, liquids are not the only fluids; gases are too. Viscosity is a measure of how much fluids resist flowing or changing their shape. The greater the viscosity, the more it resists change, and the more force must be applied to make it change. Namely, higher-viscosity fluids are thicker, gooier, or less runny. Viscosity depends on temperature and chemical structure. Examples are: High viscosity, for example, magma (molten rock in the Earth) Medium viscosity, for example, water Low viscosity, for example, air Strain. Strain is the change in shape or size (i.e., the deformation) of a solid object. Types of strain are: Elastic. The ability of an object to change shape (i.e., deform) when forced, but to spring back to its original shape when the force is released. For example: rubber band, spring Plastic. The ability to permanently change shape or deform when forced. For example: ice in glaciers, soft metals, even some rocks Properties of materials based on their ability t
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