Physical Geology GE 111 PDF

# Physical Geology GE 111 ## The Science of Geology - Geology is the study of the Earth, including the materials that it's made of, the physical and chemical changes that occur on its surface and in its interior, and the history of the planet and its life forms. - Geologists explore the Earth for...

# Physical Geology GE 111 ## The Science of Geology - Geology is the study of the Earth, including the materials that it's made of, the physical and chemical changes that occur on its surface and in its interior, and the history of the planet and its life forms. - Geologists explore the Earth for the resources needed in our technological world: - Fossil fuels such as coal, petroleum, and natural gas - Mineral resources such as metals - Sand and gravel - Fertilizers - Some search for water in reservoirs beneath Earth's surface. ## The Earth and Its Materials - The Earth's radius is about 6370 kilometers. - Most of the Earth is composed of rocks. ### Earth's Layers - **Biosphere:** All life is concentrated at or within a few kilometers of the surface. - **Hydrosphere:** The deep ocean floor is 5 km deep. Fresh water and ice exist on land. - **Atmosphere:** 99% of the atmosphere lies within 30 km of the surface. - Figure 1-1: Most of the Earth is solid rock, surrounded by the hydrosphere, the biosphere, and the atmosphere. ## Internal Processes - Processes that originate deep in the Earth's interior are called internal processes. - These are the driving forces that raise mountains, cause earthquakes, and produce volcanic eruptions. ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 ## Geologic Time - In the middle ages, scientists were influenced by the idea of the Bible stating that the Earth was created 6000 years ago, but this couldn't explain many geological events occurring on our planet. - After many researches, geologists estimated that the Earth is about 4.6 billion years old. ## The Geologic Time Scale - Geologists have divided Earth's history into units displayed in the geologic time scale. - The units are called eons, eras, periods, and epochs. ### Table 1-1: The Geologic Time Scale | Eon | Era | Period | Epoch | Distinctive Plants and Animals | |---|---|---|---|---| | Phanerozoic | Cenozoic | Quaternary | Recent or Holocene Pleistocene | Humans | | | | | Pliocene Miocene | Mammals develop and become dominant | | | | | Oligocene | Extinction of dinosaurs and many other species | | | | Paleogene | Eocene Paleocene | First flowering plants, greatest development of dinosaurs | | | Mesozoic | Cretaceous | | First birds and mammals, abundant dinosaurs | | | | Jurassic | | First dinosaurs | | | | Triassic | | Extinction of trilobites and many other marine animals | | | Paleozoic | Permian | | Great coal forests; abundant insects, first reptiles | | | | Pennsylvanian | | Large primitive trees | | | | Mississippian | | First amphibians | | | | Devonian | | First land plant fossils | | | | Silurian | | First fish | | | | Ordovician | | First organisms with shells, trilobites dominant | | | | Cambrian | | First multicelled organisms | | Proterozoic | | | | Sometimes collectively called Precambrian | | | | | | First one-celled organisms | | | | | | Approximate age of oldest rocks Origin of the Earth | | Archean | | | | | | Hadean | | | | | ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 ## Surface Processes - Surface processes are all of those processes that sculpt the Earth's surface. - Most surface processes are driven by water, although wind, ice, and gravity are also significant. ## The Hydrosphere - The hydrosphere includes: - Water in streams, wetlands, lakes, and oceans - Frozen water in glaciers - Groundwater present in soil and rock to a depth of at least 2 kilometers. - The oceans cover more than 70 percent of our planet. ## The Atmosphere - The atmosphere is a mixture of gases, mostly nitrogen and oxygen. - It is held to the Earth by gravity and thins rapidly with altitude. - Ninety-nine percent is concentrated within 30 kilometers of the Earth's surface. ## The Biosphere - The biosphere is the thin zone near the Earth's surface that is inhabited by life. - It includes the uppermost solid Earth, the hydrosphere, and the lower parts of the atmosphere. - Paleontologists are geologists who study the evolution and history of life by examining fossils and other evidence preserved in rock and sediment. ## Uniformitarianism and Catastrophism - (James Hutton, Scotland, in the late 1700s) - The principle states that geologic change occurs over long periods of time, by a sequence of almost imperceptible events. - Hutton surmised that geologic processes operating today also operated in the past. - Thus, scientists can explain events that occurred in the past by observing changes occurring today. - "The present is the key to the past." - William Whewell wrote that the geologic past may have "consisted of epochs of paroxysmal and catastrophic action, interposed between periods of comparative tranquility." - Whewell was unable to give examples of such catastrophes. - Today, geologists know that both Hutton's uniformitarianism and Whewell's catastrophism are correct. - Thus, over the great expanses of geologic time, slow, uniform processes are significant, but improbable, catastrophic events radically modify the path of slow change. ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 ## The Earth's Origin - Scientists think that 5000 million years ago, the matter that became the solar system was a very big cloud of frozen dust and gas rotating in space, consisting mainly of hydrogen and helium, the most abundant elements in the universe. - Small particles were attached by gravitational forces to make a sphere. - Some scientists said that a neighboring star exploded and caused the disc to collapse and form the "Protosun" which gained heat from collisions among the particles. - Then the gases outside the disc condensed forming small aggregates and stuck together to form big bodies with other attracted particles through gravitational forces. - This formed small rocky spheres called "planetesimals" from a few kilometers to 100 km in diameter, and then stuck together to form planets, including the Earth. - The protosun was in the center and the planetesimals on the outside. - Nuclear fusion caused heavy minerals to concentrate in the center of the Earth. ## The Modern Solar System - The heat from the sun boiled most of the hydrogen, helium and other elements from the inner solar system. - As a result, the four planets closest to the sun (Mercury, Venus, Earth, and Mars) are mainly rocky, known as terrestrial planets and are similar to the Earth, having rocky and metallic cores. - The other four planets, including Jupiter, Saturn, Uranus, and Neptune, are known as Jovian Planets, and are composed of liquids and gases with small rocky and metallic cores. ## The Evolution of the Modern Earth - Scientists agree that the Earth formed by the accretion of small particles and know that the modern earth is layered. - The center is hot and dense, known as the core, composed of iron and nickel. - The mantle is solid and it surrounds the core, composing 80% of the earth's volume. - The crust is a thin rocky surface covering the sphere. - The earth temperature and pressure increase gradually with depth. - The mantle rocks are so hot that some become melted making the mantle to flow on it, allowing the continents to move across the globe and mountains to form and oceans to open and close. - After the mantle, in the core the heat is higher, but the pressure prevents it from melting. - The outer core is composed of molten material, but the inner core, where the pressure is very high, is solid. - Figure 1-11: A schematic view of the interior of the Earth. ## Another Hypothesis - Another hypothesis states that the rock and metal accumulate simultaneously during the initial coalescence at the homogeneous, non-layered planet. - The young Earth became hot as gravity pulled the small particles together and later as asteroids, comets and planetesimals crushed into the surface. - At the same time, radioactive mineral decay heated the Earth's interior. - Heat caused most of the new Earth to melt. - Heavy molten material as iron and nickel sank to the center to form the core, while lighter material floated to form the mantle. - In both hypotheses, the crust formed later. - By studying modern meteorites and lunar rocks, we knew that the core formed at least 62000 million years ago, after the Earth coalesced together, supporting that the initial Earth was homogeneous and then separated. ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 ## Divergent Plates Boundaries (Rift Zone and Spreading Centers) - Happens when two lithospheric plates spread apart. - The underlying asthenosphere goes up to fill the space. - Magma rises the Earth's surface, where it cools and forms a new crust. - These happen below the seas, because the divergent plate boundaries are beneath seas. - Both lithosphere and asthenosphere have the same chemical composition, they differ only in strength. - When new crust forms it is like the old crust. ## The Mid-Oceanic Ridge (Rifting in the Oceans) - Mid-Oceanic Ridges form because the hot newly-formed asthenosphere rises up through the spreading center, forming the mountain under the sea. - As the molten magma drifts away, it cools and becomes dense and thick, thus making a ridge high at the center and low away from it. ## Convergent Plates Boundaries - When two lithospheric plates move toward each other. - It takes place in: - Oceanic plate vs Oceanic plate. - Oceanic plate vs Continental plate. - Continental plate vs Continental plate. - The density determines what happens - The denser plate goes under the lighter plate. - This is called **Subduction**. - Generally only oceanic lithosphere can sink into the mantle. ## Subduction Zone - A subduction Zone is a long zone where the lithospheric plate sinks into the mantle. - Rocks on the seafloor are not older than the Cretaceous because old crust is subducted and then consumed. - New crust replaces it. ## Types of Convergence - **1. Oceanic plate vs Continental plate** - The denser oceanic plate subducts into the mantle under the continent. - Many subduction zones are located at the continental margins, e.g. Subduction zone today located along the coast of Western United States and South America. - **2. Oceanic plate vs Oceanic plate** - The older oceanic crust is denser and colder, so it sinks under the younger crust. - This type is common in the Pacific Ocean. - **3. Continental plate vs Continental plate** - Both plates are light, so they don't sink, but they crumple into each other and build high mountains, e.g. The Himalaya. ## Transform Plate Boundaries - These happen when two plates slide horizontally past each other in opposite direction. - e.g. San Andreas Fault, California ## Consequences of moving Plates ### 1. Volcanoes - Volcanoes take place when hot magma rises above the surface. - They can take place in divergent and convergent plates. #### There are factors that melt rocks and make magma rise: - a. Temperature rise (Ex. East African Rift). - b. Pressure decrease. - c. Cold and dense crust subducting down makes it hotter, so it melts and causes magma to rise up. ### 2. Earthquakes ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 ## The Earth's Interior (Layers) - (see figure 2-2, 2-3, 2-4) ### 1 The Crust - The crust is the outermost and thinnest layer. - Because the crust is relatively cool, it consists of hard, strong rock. - Crust beneath the oceans differs from that of continents. #### A. The Continental Crust - It is the cool and hard outermost layer. - Thickness may reach 20-40 Km, but in some mountains it may be 70 Km. - Granitic in composition (light minerals) #### B. The Oceanic Crust - Thin (5-10 Km) - Basaltic in composition (dark minerals) ### 2. The Mantle - Directly under the crust, making up 80% of the Earth's volume (2900 km). - Its chemical composition is relatively similar, but the temperature and pressure change with depth. - These changes the strength of the rocks, forming layers. - The uppermost mantle and the crust form the **Lithosphere**. #### A. The Lithosphere - Cool and hard. - 75-125 km thick, in divergent places it is only 10 km. - It is divided into tectonic plates. #### B. The Asthenosphere (Plastic) - It is weak layer under the hard lithosphere. - This change is caused by increasing temperature with depth. - This causes 1-2% of the asthenosphere to be liquid and plastic. - This condition exists from the base of the lithosphere to about 350 km, after that it becomes mechanically strong due to the increasing pressure. ## 3. The Core - Innermost part of the Earth's layer (6000 C°). - It is a sphere with a radius of about 3470 km. - Composed largely of iron and nickel. - The outer core is molten (high temperature). - Figure 2-2: Plates of lithosphere glide over the asthenosphere, carrying continents and oceans with them. As a plate moves, old lithosphere sinks into the Earth's interior at its leading edge. And new lithosphere forms at the trailing edge. ## Plates and Plate Tectonics (See Figs: 2-5 to 2-9) - Because the lithosphere has lower density, the asthenosphere floats above it. - The lithosphere is broken into 7 major plates and many microplates. - These plates move slowly (1-6 cm/year), and may hit each other. - Forces from collision build mountains, make volcanic eruptions and earthquakes. - Different types of collisions make different tectonics. ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 ## Gravity - Sliding away magma from the mid-oceanic ridges moves down along a considerable slope. - It cools and become denser until it hits the continental margin, and subducts down pulling the rest of the plate with it. - This is called the push-pull theory. ## Mantle Plumes - The push-pull model provides a mechanism to maintain plate movements once movement had started. - However, it doesn't explain how they start movements in the first place. - The hot plume starts as a hot rising column of plastic rocks that originate deep into the mantle. - This happens when some rocks in some parts of the mantle become hotter than all surroundings. - (Heat may come from the core or radioactive minerals). - When large quantity of magma plumes, they form volcanoes at locations called **Hot Spots**. - These may shot up and form islands like Hawaii. - Some geologists suggested that hot plumes may form new spreading centers, which will initiate movement and then the push-pull mechanism can work. ## Supercontinents - Movement on tectonic plates cause continents to collide and stick together to form a supercontinent (e.g. Pangea). - This will break up and give separate continents, which may collide again and form another Pangea and so on. ## Isostasy (Vertical Movement) - When more lithosphere is added, the crust sinks and underlying asthenosphere moves laterally away from the heavy region to give way to the added lithosphere. - Suppose large a large glacial melts, the lithosphere becomes heavier and moves down. - This is known as **Isostasy**, and the accommodation of this vertical movement by the earth's crust is known as **isostatic equilibrium**. - Pangea -> Laurasia -> Gondwana ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch3 ## Table 3-4: The Minerals of the Mohs Hardness Scale | Minerals of Mohs Scale | Common Objects | |---|---| | Talc | Fingernail | | Gypsum | Copper penny | | Calcite | Knife blade | | Fluorite | Window glass | | Apatite| Steel file| | Orthoclase | | | Quartz | | | Topaz | | | Corundum | | | Diamond | | ## 4. Cleavage - Cleavage is the tendency of some minerals to break along flat surfaces (along weak planes). - **Example:** Mica and graphite, have one set of parallel cleavage planes. - Other minerals have two, three, or even four different sets. - Many minerals have no cleavage at all. ## 5. Specific Gravity - Specific gravity is the weight of a substance relative to that of an equal volume of water. - **Example:** A mineral with specific gravity of 2 will weigh twice the volume of water. ## 6. Color - It is the color a pure mineral will give, but it is commonly unreliable for identification because most minerals are not pure. ## 7. Streak - Streak is the color of a fine powder of a mineral. - It is observed by rubbing the mineral across a piece of unglazed porcelain known as a streak plate. ## 8. Luster - Luster is the manner in which a mineral reflects light. - This could be glassy, pearly, earthy, or resinous. ## 9. Transparency - It is the ability of mineral to pass light. - Minerals can be transparent, translucent, or opaque. ## Rock-Forming Minerals - Although about 3500 minerals are known to exist in the Earth's crust, only a small number (50 and 100) are important because they are common or valuable. - The most important minerals for geologists are olivine, pyroxene, amphibole, mica, the clay minerals, feldspar, quartz, calcite, and dolomite. - The first six minerals in the above list are actually mineral "groups" in which each group contains several varieties. - Each forms a group because they have very similar chemical compositions, crystalline structures, and appearances. ### Accessory Minerals - Accessory minerals are minerals that are common but usually are found only in small amounts. - These include chlorite, garnet, hematite, limonite, magnetite, and pyrite. ### Gems - These are minerals with beautiful appearances, such as Diamond and Rubies. ### Ore Minerals - Ore minerals are minerals from which metals or other elements can be recovered with profit, such as copper, lead, and zinc. ### Industrial Minerals - Some minerals may not be ores, but have some importance for the industry, such as Halite, Gypsum, Apatite and Calcite. ## Classification of Minerals ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch3 ## Crystal Habit - Crystal habit is the characteristic shape of a mineral and the manner in which aggregates of crystals grow. ## 2. Fracture - It is the pattern in which a mineral breaks. - Minerals may give: - **Conchoidal Fracture (Fig. 3-10), e.g. quartz and olivine.** - **Splintery or fibrous Fragments, e.g. graphite. ** - **Smooth Fracture with soft face. ** - **Irregular Fracture with rough face. ** - Figure 3-10: Conchoidal fracture ## 3. Hardness - It is the ability of mineral to resist scratch. - To measure hardness more accurately, geologists use a scale based on ten minerals, numbered 1 through 10. - Each mineral is harder than those with lower numbers on the scale, so 10 (diamond) is the hardest and 1 (talc) is the softest. - The scale is known as the Mohs scale of hardness. - **Mohs scale of hardness (Table 3-4)** ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch3 - Geologists classify minerals according to their anions (negatively charged ions). - Anions can be simple or complex. - Simple anions have simple charge, e.g. o-2. - Complex anions are composed of two or more atoms, which bond together as in: - silicates (SiO4), or carbonates (CO3)2. - Each mineral group (except the native elements) is named for its anion: - For example, the oxides all contain negative oxygen (O²), the silicates contain negative silicon (SiO4)-4, and the carbonates contain negative carbon (CO3)2. - ## Native Elements - Occur naturally in their native states as minerals. - They make about 20 minerals. - Fewer than ten are common enough to be of economic importance. - Gold, silver, platinum, and copper are all mined in their pure forms. - Others like Iron, carbon, and silver are less common. ## Oxides - The oxides are a large group of minerals in which oxygen is combined with one or more metals. - Oxide minerals are the most important ores of iron, manganese, tin, chromium, uranium, titanium, and several other industrial metals. - Hematite (iron oxide, Fe2O3) occurs widely in many types of rocks and is the most abundant ore of iron. - Magnetite (Fe3O4), a naturally magnetic iron oxide, is another ore of iron. - Ice, the oxide of hydrogen (H2O), is a common mineral at the Earth's surface. ## Sulfides - Sulfide minerals consist of sulfur combined with one or more metals. - Sulfides are the world's major sources of copper, lead, zinc, molybdenum, silver, cobalt, mercury, nickel, and several other metals. - The most common sulfides are pyrite (FeS2), chalcopyrite (CuFeS2), galena (PbS), and sphalerite (ZnS). ## Sulfates - The sulfate minerals contain the sulfate complex anion (SO4)2. - Gypsum (CaSO4_2H₂O) and anhydrite (CaSO4) are two important industrial sulfates. - Both form by evaporation of seawater or salty lake water. ## Phosphates - Phosphate minerals contain the complex anion (PO4)3. ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch 3 - The nucleus becomes stable when the outermost shell is filled with electrons. - These electrons can be lost or gained and make the nucleus negative if they are more than the protons and vice versa. - A negatively charged atom is called an anion, and the positively charged atom is called a cation. - All the crustal elements except Oxygen release electrons to become +ve cations such as K+1, Al+3, 0-2. - Atoms often unite to form compounds. - Chemical formulas are used to express these compounds: - Ex: AlSiO4, SiO2, Ca03 - Some minerals may remain native as gold (AU) and silver (Ag). - Figure 3-2: An atom consists of a small, dense, positive nucleus surrounded by much larger cloud of negative electrons. ## Crystals: The crystalline nature of Minerals (see Fig 3-3): - A crystal is made of systematic atoms arranged in repeated pattern. - All minerals are crystalline. - Example: Halite (table salt), it forms a cube, while other minerals have different crystal forms. ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch 3 - Figure 3: Carbon atoms in diamond form a tetrahedral network similar to that of quartz. ## C. Metallic Bonds - In a metallic bond, the outer electrons are loose and can freely move from one atom to another, and result in high density bonding. E.g. Pyrite (FeS). ## D. Van der Waals Forces - Weak electrical forces called van der Waals forces also bond molecules together. - These weak bonds result from an uneven distribution of electrons around individual molecules, so that one portion of a molecule may have a greater density of negative charge while another portion has a partial positive charge. - This mostly happens in low hardness minerals, such as Talc and Graphite. ## Physical Properties of Minerals - How does a geologist identify a mineral in the field? - Chemical composition and crystal structure distinguish each mineral from all others. ## 1. Crystal Habit ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch 3 - Luster is the manner in which a mineral reflects light. - This could be glassy, pearly, earthy, or resinous. ## 9. Transparency - It is the ability of mineral to pass light. - Minerals can be transparent, translucent, or opaque. ## Rock-Forming Minerals - Although about 3500 minerals are known to exist in the Earth's crust, only a small number (50 and 100) are important because they are common or valuable. - The most important minerals for geologists are olivine, pyroxene, amphibole, mica, the clay minerals, feldspar, quartz, calcite, and dolomite. - The first six minerals in the above list are actually mineral "groups" in which each group contains several varieties. - Each forms a group because they have very similar chemical compositions, crystalline structures, and appearances. ### Accessory Minerals - Accessory minerals are minerals that are common but usually are found only in small amounts. - These include chlorite, garnet, hematite, limonite, magnetite, and pyrite. ### Gems - These are minerals with beautiful appearances, such as Diamond and Rubies. ### Ore Minerals - Ore minerals are minerals from which metals or other elements can be recovered with profit, such as copper, lead, and zinc. ### Industrial Minerals - Some minerals may not be ores, but have some importance for the industry, such as Halite, Gypsum, Apatite and Calcite. ## Classification of Minerals ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch3 - Apatite, Cas(F,CI,OH)(PO4)3, is the substance that makes up both teeth and bones. - Phosphate is an essential fertilizer in modern agriculture. ## Carbonates - The complex carbonate anion (CO3)-2 is the basis of two common rock-forming minerals, calcite (CaCO3) and dolomite [CaMg(CO3)²]. - Aragonite is a polymorph of calcite that makes up the shells of many marine animals. ## Silicates - The silicate minerals contain the (SiO4)-4 complex anion. - Silicates make up about 95% of the Earth's crust. - They are so abundant for two reasons: - First, silicon and oxygen are the two most plentiful elements in the crust. - Second, silicon and oxygen combine readily. ## Structure of silicates - Every silicon atom surrounds itself with four oxygens with a very strong bond. - The silicon atom and its four oxygens form a pyramid-shaped structure called the silicate tetrahedron with silicon in the center and oxygens at the four corners (Fig.3-17). - The silicate tetrahedron has a (-4) charge and forms the (SiO4)-4 complex anion. - The silicate tetrahedron is the fundamental building block of all silicate minerals. - Figure 3-17: The silicate tetrahedron consists of one silicon atom surrounded by four oxygens. It is the fundamental building block of all silicate minerals. (a) A ball-and-stick representation. (b) A proportionally accurate model. ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch 3 - A rock is an aggregate of minerals. - Some rocks are made of only one mineral, but most contain two to five abundant minerals plus minor amounts of several others. ## A mineral has these characteristics: - Natural occurrence. - Inorganic solid material. - Chemical composition. - Crystalline structure. - Characteristics 3 and 4 are the two most important because they distinguish any mineral from all others. ## Chemical Composition (Elements & Atoms) - Elements are small and cannot be broken into other simple particles. - There are 88 elements occurring in nature, but O2, Al, Si, Fe, Ca, Mg, K, Na are the most common rock-forming minerals and form 98% of the crust. ## Atoms (see Fig 3-2) - An atom is the basic unit of an element. - The Average diameter is 10-10 meter. - It has a nucleus surrounded by negative electrones. - Electrons orbit the nucleus in shells. Each shell can hold a certain number of electrons. ### A nucleus has: - **Neutrons; neutrally charged. ** - **Protons; positively charged. ** ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch 3 - EX: when sodium (Na+) and chlorine (Cl) form an ionic bond, the sodium atom loses one electron to become a cation and chlorine gains one to become an anion. - When they combine, the +1 charge balances the -1 charge. - Figure 2: When sodium and chlorine atoms combine, sodium loses one electron, becoming a cation, Na+. Chlorine acquires the electron to become an anion, Cl-. ## B. Covalent Bonds - A covalent bond develops when two or more atoms share their electrons to fill the outer electron shells. - For example, carbon needs four electrons to fill its outermost shell. - It can achieve this by forming four covalent bonds with four adjacent carbon atoms. - It "gains" four electrons by sharing one with another carbon atom at each of the four bonds. - Diamond consists of a three-dimensional network of carbon atoms bonded into a network of tetrahedra, similar to the framework structure of quartz. ## Text Book: Introduction to Physical Geology, Thompson & Turk # Physical Geology GE 111 Ch 3 - Figure 3-3: The orderly arrangement of sodium and chlorine ions in halite. ## A crystal face - A crystal face is a planar surface that develops if a crystal grows freely in an uncrowded environment. ## Chemical bonds: - Four types of chemical bonds are found in minerals: ionic, covalent, metallic, and van der Waals forces. ## A. Ionic Bonds - Cations and anions are attracted by their opposite electronic charges and thus bond together. - An ionic compound (made up of two or more ions) is neutral because the positive and negative charges balance each other. ## Text Book: Introduction to Physical Geology, Thompson & Turk