Chapter 1 and 3 Notes
Chapter 1 and 3 Notes EAR 110 - M010
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1 An Introduction To Geology Notes 11 Geology The Science of Earth 0 Geology is the science working to achieve an understanding of the Earth 0 Earth is constantly changing from the submicroscopic to global scale and as rapid as a natural disaster or slow enough to change over the course of multiple lifetimes Physical and Historical Geology 0 This textbook focuses on physical geology examines the materials that make up the Earth and try to understand Earth s processes beneath and on the surface 0 Historical geology focuses on Earth s past and the chronological arrangement of physical and biological changes Earth has gone through to get where it is now 0 You MUST understand physical geology to understand historical geology because quotwe must understand how the Earth works to unravel its pastquot 0 Most geology is studied outdoors but laboratory is necessary for research on the microscopic levels Geology People and the Environment 0 Natural hazardsdisasters are a huge deal to people oods tsunamis volcanoes earthquakes landslides but these are natural processes of Earth that only become hazards when people live where they occur Urbanization is a growing threat to natural disaster because it not only condenses millions of people into megacities but the building of these megacities often destroys natural defenses against natural disasters like wetlands and sand dunes Poorly constructed buildings and inappropriate land use combined with rapid population growth increase vulnerably Earths natural resources have been the tools used to build modern civilization soil water metallicnonmetallic minerals Human presence has cause natural system s inability to adjust to the arti cial changes we make eg Deforestation cities and dams have caused frequent ooding 12 Development of Geology 0 Aristotle s ill proven but widely believed explanations of natural disasters began to be disproven in the Renaissance of 15005 Catastrophism In the mid 16005 James Ussher Archbishop of Ireland a respected biblical scholar published work on the chronology of the Earth that calculated its age to be a few thousand years old Ussher s ideas greatly in uenced catastrophism a doctrine that believed Earth s landscapes were the product of great catastrophes quotMountains and canyons that took great spans of time to form were thought to have been formed in sudden and often worldwide disastersquot which supported the philosophy that greatly underestimated Earth s age The Birth of Modern Geology 0 James Hutton Scottish physician and farmer published Theory ofthe Earth in 1795 which sparked the fundamental principal of uniformitarianism stating that the physical chemical and biological laws that operate today have also operated in the geologic past 0 To understand Earth s ancient landscapes we must understand presentday processes and their results OR the present is key to the past and future Forces that appear small can over a long period of time produce equally as great of results as that of a catastrophe Mountains are sculpted and destroyed by weathering and work of running water that carries mountain waste into oceans Geology Today Hutton s theory does not mean that the processes in the past always had the same importance or operated at the same rate as they do today 0 Some geological processes are not observable but evidence that they occur is well established eg Meteorites evidence but no witnesses Hutton s most famous quote is quotThe results therefore of our present inquiry is that we nd no vestige of a beginning and no prospect of an endquot The Magnitude of Geologic Time 0 Geology anazlyes time millions of years before the present to the present 0 We will examine events over the spans of centuries 13 The Nature of Scienti c Inquiry The goal of science is to discover and predict the underlying patterns in nature and use them to our advantage eg Predicting the most probable spots for oil to maximize searching time Hypothesis 0 To try to explain why or how things happen in the manner observed geologists develop hypothesis a tentative or untested explanation The hypothesis MUST be able to be tested and tested through comparison with objective observations of nature Many hypothesis are discarded and to state simply quotscience is the acceptance of what works and the rejection of what does notquot Theory After a hypothesis has gone through the scrutiny of objective observation and eliminated its competitors it is then considered scienti c theory a well tested and widely accepted view that the scienti c community agrees best explains certain observable facts Many theories some simply impossible to have 100 proof of have extensive support and are well comprehended and believed eg Plate tectonics explain earthquakes mountains and volcanic activity Scienti c Methods Scienti c method is the process in which scientists gather facts through observations and formulate scienti c hypotheses and theories It s not a structured step my step process anymore instead it involves a lot of creativity and insight but it does involve the following o A question is raised about the natural world 0 Scienti c data that relate to the question are collected 0 Questions that relate to the data are posed and one or more working hypotheses are developed that may answer the question 0 Observations and experiments are developed to test the hypothesis 0 The hypothesis are accepted modi ed or rejected based on extensive testing 0 Data and results are shared with scienti c Plate Tectonics In the early 20th century the revolution of our understanding of Earth started when the theory of continental drift was proposed the idea that continents move about the face of the planet There was a lot of controversy and through proof the theory of plate tectonics aroused which gave geologists the rst comprehensive model of earth s internal workings Earth s Spheres The physical environment of Earth is divided into the hydrosphere the water portion of our planet the atmosphere Earth s gaseous envelope and the geosphere solid earth The environment is not dominated by either portion instead it is characterized by each one s interaction with one another o The biosphere the totality of all plant and animal life on our planet interacts with each of the physical characteristics and is equally integrated Interactions between the four realms are incalculable Hydrosphere 0 Water makes earth unique 0 The hydrosphere is a dynamic mass of water that is continually on the move because of evaporation precipitation o The ocean the most prominent of the realms taking 71 of surface and averaging 3800 ft in depth but the hydrosphere also accounts for underground freshwater streams lakes and glaciers Atmosphere 0 The atmosphere is the lifegiving gaseous envelope that surrounds the earth 0 Though it seems large compared to the earths diameter it is small o It provides the ear we breathe and protects us from the suns intense heat and dangerous ultraviolet radiation 0 Energy exchanges that continually occur between atmosphere and space produce weather and climate climate having an intense effect on nature and intensity of Earth s external processes o If we had no atmosphere our planet would be lifeless and many of the processes and interactions that make the surface dynamic couldn t operate Biosphere o This includes all life on earth which is generally towards the surface ocean life is concentrated in sunlit surface waters land life is generally under a kilometer high 0 Some exotic lifeforms live in extreme environment like ocean oor lifeforms 0 Without life the makeup and nature of all of Earth s other realms would be different Geosphere The geosphere is the solid earth extending from the surface to the center of the planet 6400 kilometers the largest of the four spheres 0 We examine prominent surface features and their global extent to obtain clues to the processes that have shaped our planet 0 Soil is not a part of the for spheres simply a smaller part of the geosphere and a mixture between rock debris and organic matter from decayed plant and animal life 15 Earth as a System Ea rth System Science Interactive processes between the hydrosphere atmosphere and geosphere have a HUGE impact on the biosphere eg Excessive precipitation caused mudslides that buried densely populated parts of Zhouqo killing 1500 System science views and observes Earth as a system composed of numerous interacting subsystems 0 Earth system science integrates geology atmospheric science chemistry biology and several other academic elds A system is a group of interacting or interdependent parts that form a complex whole The Earth System 16 The hydraulic system is when water evaporates from earth s surface and transpiration from plants condenses to form couds then precipitates to fall back onto the surface The rock cycle is the process by which one rock changes to another The carbon cycle is the interaction ow between the carbon dioxide in air and the carbon in living things in certain sedimentary rocks All of earths systems are linked so that a change in one part produces changes in any or all other parts Earths processes can vary on special scaes form fractions of millimeters to thousands of kilometers and time ranges from milliseconds to billions of years but no matter the variation many processes many are connected and in uence many components in other systems The earth s system is powered 2 sources 0 The sun39s energy drives weather and climate ocean circuationa nd erosional processes 0 Earth39s interior heatenergy from radioactive decay produce volcanoes earthquakes and mountains Early Evolution of Earth Origin of Planet Earth The Universe Begins in the Big Bang Theory 137 billion years ago an incomprehensibly arge explosion sent all matter of the universe ying outward at incredible speeds Debris from the explosion hydrogen and helium began to cool and condense into the rst stars and galaxies The Solar System Forms Earth and the other planets were formed at the same time and from the same primordial material as the Sun o The nebular theory proposes that bodies of our solar system evolved from an enormous rotating cloud called solar nebula 0 Solar nebula consists of helium and hydrogen from the big bang as long as dust grains and ejected matter of long dead stars 0 5 billion years ago the cloud began to contract due to gravitational interactions among its particles then was triggered to collapse by a shockwave from a catastrophic explosion supernova o The force causes the nebula to spin and eventually atten out into a disc shape with a large concentration of material at its center called the protosun presun 0 During the collapse gravitational energy was turned into heat which led to the creation of the Sun 0 Inner Planets Form 0 After the sun was formed the temperatures began to decline and cause substances with high melting points to condense into tiny particles and join together 0 Rock forming minerals formed metallic and rocky clumps that orbited the sun and repeat collisions caused masses to combine into large asteroidsized bodies called planetesimals which in 105 of millions of years eventually became Mercury Venus Earth and Mars 0 Not all rocky clumps were recognized as planets but when they collide with earth they are meteorites o The inner planets weren t able to accumulate lighter components of the nebular cloud because of relatively high temperatures and weak gravitational elds 0 Outer Planets Develop At the same time the inner planets were developing the materials which contained a high percentage of ices water carbon dioxide ammonia methane as well as rocky and metallic debris drifted and created the outer planets because of such low temperatures Formation of Earth s Layered Structure 0 As material accumulated to form earth high velocity of nebular debris and radioactive decay caused Earth s temperature to rise 0 Iron and nickel other metallic elements began to melt and liquid blobs of dense metal sank towards the center of the planet to create Earths dense ironrich core 0 Chemical Differentiation and Earth s Layers buoyant masses of molten rock began to form at the surface and were combined by silicone aluminum and some calcium sodium potassium iron and magnesium Also gold lead and uranium which have low melting points joined the surface 17 o The early periods of chemical differentiation established Earth s divided interior the ironrich core the thin primitive crust and the mantle which is located between the core and the crust An Atmosphere Develops gaseous materials escaped from the earth s interior today through volcanic eruptions and the atmosphere evolved Continents and Ocean Basins Evolve it s general agreement that continental crust formed gradually over the past 4 billion years Earth s Internal Structure Monitoring stations are set up all over the world to gather and analyze earthquake data to build a detailed picture of earth s interior based off of energy penetration Earth s Crust The crust is the relatively thin surface of the planet made up of continental crust land and oceanic crust sea bottom 0 Oceanic crust is approx 7km thick and composed of dark igneous rock basalt and is considerably denser and younger than continental crust 0 Continental crust is 3570km thick and consists of many rock types though upper crust has an average composition of granitic rock called granodiorite Earth s Mantle 82 of earth s volume is contained in the mantle a solid rocky shell with a depth of 2900km The separation between crust and mantel is a chemical composition change mantel is made of peridodite richer in magnesium and iron than any of the surface rocks Upper Mantle The top portion of the upper mantel id divided into 3 different parts the stronger lithosphere the weaker asthenosphere and the bottom called the transition zone 0 The lithosphere sphere of rock consists of the crust and the uppermost mantle averaging from 100250km thick 0 The asthenosphere quotweak spherequot 250410km below the Earth s surface consists of slightly melted rock and is mechanically detached from the layer above allowing for the lithosphere to move independently o The transition zone about 410660im below the surface is identi ed by a sudden increase in density from about 35 to 37 gcmquot3 because minerals in peridotite respond to the increase in pressure by forming new minerals with closely packed atomic structures Lower Mantle from 660km2900km below the earth s surface is the lower mantle The lower mantle gradually strengthens with depth due to pressure and the rock is capable of extremely gradual ow The lowest part of the mantel is called the quotdquot layer or dee doubleprime which is a highly variable and unusual layer Earth s core 18 The core is though to be composed of ironnickel alloy with minor amounts of oxygen silicon and sulfur elements that readily form compounds with iron The outer core is a liquid layer 2700km thick and the movement of metallic iron within this zone creates Earth s magnetic eld The inner core is a sphere with a radius of 1216km and is solid due to immense pressures that exist in the center of the planet Rocks and the Rock Cycle The minerals that compose it strongly in uence the nature and appearance of a rock also texture size shape and arrangement of constituent minerals o A rocks mineral composition is the re ection of the geological processes that created it Geologists divide rocks into three major groups igneous sedimentary and metamorphic The rock cycle helps us view the many of the interrelationships among different parts of the Earth s system and helps understand the origin of each type of rock The Basic Cycle Magma molten rock that forms deep beneath the Earth s surface cools and solidi es in a process called crystallization either beneath the earths surface or after a volcanic eruption resulting in igneous rocks After weathering the rock is decomposed and moved downslope by gravity eventually picked up and dissolved into sediment Sediments undergo lithi cation or quotconversion into rockquot into sedimentary rock when compacted by weight of overlying layers or cemented as groundwater lls the pores with mineral matter When sedimentary rock is buried deep in the crust heat and pressure stress change it to metamorphic rock Metamorphic rock melts to magma when more heat and pressure is added and the cycle starts all over again Alternative Paths Deeply buried igneous rocks subject to high temperatures and pressure transform directly into metamorphic rock Metamorphic and sedimentary rocks may not remain buried and instead become stripped and attacked by weather and turned into raw materials for sedimentary rocks 19 The Face of Earth Continents are remarkably at with the presence of plateaus protruding above sea level Continent elevation averages 8km and remains close to sea level excluding mountain terrain 37gcm3 The average depth of ocean basins is 38km below sea level The basalt is 7km thick and 30gcm3 thick 0 Continental crust is more buoyant that oceanic crust Major Features of the Continents Mountain Belts the youngest mountains are located in the circumPacific belt which include the western American mountains and island arcs active mountain regions composed largely of volcanic rocks and deformed sedientary rocks like Japan Philippines New Guinea that extend into the Paci c 0 Another major mountain belt extends eastward through the Alps trhough lran nd the Himilayas and southward into lndonega 0 Most mountain terrains are places where thick sequences of rocks have been squeezed and highly deformed 0 Older mountains are the Appalachians and the Eastern US and Urals in Russia worn low through millions of years of weathering 0 Stable Interior The interior of continents called cratons have been relatively stable for the past 600 million years 0 Within stable interiors are areas known as shields which are expansive at regions composed largely of deformed igneous and metamorphic rock Shields are ancient containing 14 billion year old rocks 0 Stable platforms are another at area which are highly deformed rocks like those found in shields covered by a thin layer of sedimentary rocks They are ususlly nearly horizontal unless they re warped to form large basins or domes Major Features of the Ocean oor 0 Three major regions of the ocean oor continental margins deepocean basins and oceanic midocean ridges Continental Margin is the portion of the sea oor adjacent to major landmasses including the continental shelf the continental slope and the continental rise 0 The continental shelf is an extension of the continental land underwater a ooded extension of the continets o The continental slope is a relatively steep dropoff acts as a boundary between the continents and deep ocean basins It extends from the outer edge of the continental shelf to the oor of the deep ocean basin 0 The slope is then met by a continental rise a thick wedge of sediment that moved downslope from the continental shelf and accumulated on the deep ocean oor 0 Deep Ocean Basins lie between the continental margins and oceanic ridges o Abyssal plains are increadibly at features of the basins 0 Deep ocean trenches are extremely deep depressions that are occasionally more that 11000m deep Though they are a small fraction of the ocean core they often lie adjacent to young mountains and island chains where they would be called volcanic island arcs o Seamounts are submerged volcanic structures which sometimes form long narrow change Volcanic activity forms large lava plateaus which can be composed of continentaltype crust Oceanic Ridges are the most prominent feature on the ocean oor including the oceanic ridge and the midocean ridge 0 The MidAtlantic Ridge and the East Paci c Rise are parts of this system The elevated features form a contious belt that winds more that 70000km around the globe similar to a baseball seam o Ridges unlike mountains consist of layer upon layer of igneous rock that has been fractured and uplifted 3 Matter and Minerals 31 Minerals Building Blocks of Rocks De ning a Mineral o A mineral is any naturally occurring inorganic solid that possesses an orderly crystalline structure and a de nite chemical composition that allows for some variation 1 Naturally occurring must form by natural geologic processes and cannot be human madeintervened 2 Generally inorganic cannot have been derived from living matter with the exception of inorganic compounds that make up animal shellscoral reefs that are buried and put in the rock cycle 3 Solid substance With the exception of mercury every mineral must be a solid Ice is a mineral but water is not 4 Orderly crystalline structure Atoms in minerals are arranged in an orderly repetitive manner 5 De nite chemical composition that allows for some variation 0 A rock is any solid mass of mineral or minerallike matter that occurs naturally as a part of the planet 0 Mostly aggregates of several minerals minerals are joined in such a way t hat their individual properties are retained 0 Some can be composed almost entirely of one mineral 0 Some rocks are composed of nonmineral matter Obsidian and pumice volcanic rocks Coal consists of noncrystalline glassy substance 32 Atoms Building Blocks of Minerals Properties of Protons Neutrons and Electrons Protons and neutrons are very dense particles with the same mass while electrons are 12000th of a proton Protons and Electrons have opposite electrical charge positive and negative Valence electrons are the outermost shellcloud of electrons that play a key role in interacting with other atoms to form chemical bonds Elements De ned by Their Numberof Protons The atomic number is the number of protons in the nucleus of an atom which determines its chemical nature 0 A group of the same kinds of atoms same atomic number therefore same chemical and physical properties is called an element 0 Elements are organized in the periodic table so that those iith similar properties line up in columns 0 Few minerals are made up of entirely one element copper diamonds sulfer gold 0 Others are chemical compounds elements that join with atoms of other elements 33 Why Atoms Bond The Octet Rule and Chemical Bonds 0 The octet rule states that quotatoms tend to gain lose or share electrons until they are surrounded by eight valence electronsquot 0 There are exceptions but it s considered the rule of thumb A chemical bond is the transfer or sharing of electrons that allows each aatom to attain a full valence shell of electrons 0 When electrons are transferred elements form an ionic bond each individual element becomes a positive or negative ion The attraction of oppositely charged ions forms a neutral ionic compound dramatically different from the original properties of the element 0 When electrons are shared between atoms it forms a covalent bond 0 Metallic bonds is when the valence electrons are free to move from one atoms to another so that the atoms share the available valence electrons Accounts for high conductivity in metals the ease in which they are shaped and other physical properties 0 Hybrid bonds exhibita some degree of electron sharing and some degree of electron transfer 34 How Do Minerals Form Precipitation of Mineral Matter 0 Drop in temperature and or water loss through evaporation cause the solution to become closer to saturation in which the ions bond and form crystalline solids that settle out of the solution 0 Minerals also precipitate from slow moving groundwater and ll in fractures and voids in rocks forming a geode a rock with inwardly projecting crystals Crystallization of Molten Rock 0 As molten rock cools the magma crystallizes and forms rock either slowly cooled with large crystals or quickly cooled with hardly visible crystals Deposition as a Result of Biological Processes Vertebrate animals use mineral ions in seawater to create external constructions When their remains are buried they become a part of massive reefs or sedimentary rock 35 Physical Properties of Minerals Optical Properties Luster is the appearance or quality of light re ected from the surface of a mineral 0 Metallic lustersubmetallic luster o Nonmetallic luster glassy vitreous Dullearthy luster Pearly luster Silky luster like satin cloth Greasy luster satin cloth 0 Ability to Transmit light opaque no light transmitted translucent light but not an image is transmitted through a mineral sample and transparent both light and image are visible 0 Color generally the most conspicuous characteristic and isn t reliable Streak Color of a mineral in powdered form obtained by rubbing it across a streak plate 0 Metallic minerals have dense dark streak o Nonmetallic has lightcolored streak Crystal Shape or Habit Refer to the common or characteristic shape of a crystal or aggregate of crystals 0 Magnetiteoctahedrons o GarnetsO dodecahedrons o Halite and uorite cubes 0 Common terms used to describe habits o Equantequidimensional o Bladed elongated crystals that are attened in one direction Fibrous thin rounded crystals that break into bers Banded minerals that have stripes or bands of different colors or texture Cubed groups of crystals shaped like cubes Tabular Prismatic Planty o Blocky Mineral Strength Tenacity a minerals toughness or its resistance to breaking or deforming does it shatter easily Is it malleable Elastic Hardness is a measure of resistance of a mineral to abrasion or scratching o Mohs Scale of Hardness relative ranking not comparative 1 Talc CO 0000 Gypsum Calcite Fluorite Apatite Orthoclase Qua z Topaz Corundum 10 Diamond Cleavage the tendency of a mineral to break cleave along planes of weak bonding 0 When minerals break evenly in more that one direction cleavage is described by the number of cleavage directions the angles in which they meet and the quality of the damage Fracture minerals that have chemical bonds that are equally or nearly equally strong in al directions fracture producing uneven surfaces and exhibiting irregular fracture Density is mass per unit of volume but mineralogists use speci c gravity to describe density of minerals dimensionless number representing the ratio of the mineral s weight to the weight of an equal volume of water Other Properties of Minerals 0 Double refraction when a transparent piece of calcite is placed over printed text Halite salt is distinguishable by taste 0 Magnetite high in iron can be picked up with a magnet o Carbonate minerals will x when dilute hydrochloric acid is dropped on it omseweww 36 Mineral Structures and Compositions Crystal or crystalline refers to any natural solid with an orderly repeating internal structure Mineral Structures 0 Some crystal structures made up of only one element gold silver consist of the same element packed in a simple three dimensional network that minimizes voids o The atomic structure of minerals with at least two different elements is arranged in unit cells cubic shapes with the positive ions surrounded by the negative ions and vice versa 0 Two minerals can be constructed of geometrically similar building blocks yet exhibit different external forms 0 Cubic cells can combine to produce different shaped crystals Steno s Law or the Law of Constancy of lnterfacial Angles states that regardless of sample size the size of the crystal faces or where the crystals are collected the angles between adjacent prism faces are consistent all the same and this applies to all minerals Compositional Variations in Minerals Ions of similar size can readily substitute for one another without disrupting the minerals internal framework with causes substantial variation of chemical composition of the same minerals o Eg olivine can have different variations of Mg and Fe balance some containing no iron or no magnesium at all and most having different combinations o It keeps the same internal structure and mostly the same physical properties but the chemical composition is different 0 Trace elements elements not originally found in the chemical make up of the mineral often alter the color of quartz and uorite but aren t very chemically different not enough to cause physical change Structural Variations in Minerals 0 Polymorphs are minerals with the exact same chemical composition that have different internal structures and hence take different external forms 0 Graphite and diamond pure carbon atoms but different minerals This is caused by the variety of conditions in which rocks form Extremely high pressures and temperatures produce compact structure shown in diamond while minerals formed at lower pressures and temperatures tend to take on looser forms shown in granite 0 Diamonds eventually form into granite when they re taken out of those conditions but it happens slowly The transformation of one polymorph to another is called phase change 37 How Minerals Are Classi ed 0 Economic minerals are used extensively in the manufacture of products but rock forming minerals are not excluded from this group or vice versa 0 Rockforming minerals are the few dozen abundant minerals that make up most of the rocks of Earth s crust Classifying Minerals Mineralogists use the term mineral species for a collection of specimens that exhibit similar internal structure and chemical compositions 0 Some mineral species are subdivided into mineral varieties eg pure quartz and amethyst are all a part of the quartz mineral Mineral species are assigned mineral classes that tend to have similar internal structure and similar properties usually found together in the same rock 0 Silicates carbonates halides and sulfates are important mineral classes Silicate Versus Nonsilicate Minerals The eight elements that make up the vast majority of rock forming minerals and represent 98 of the earth s crust are in order of abundance 0 Oxygen Silicon Aluminum lron Calcium Sodium Potassium 0 Magnesium Silicon and oxygen most abundant minerals readily combine to form the basic quotbuilding blockquot for most the most common mineral group silicates 0 Over 800 minerals belong to this group and it accounts for over 90 of earth s crust Because other mineral groups are far less abundant they re grouped and know as nonsilicates 0 Economic importance provide us with iron and aluminum for automobiles and gypsum for plaster and drywall 0 Major constituents of sediment and sedimentary rock 000000 38 The Silicates Silicate Structures The siliconoxygen tetrahedron SiO4 is the fundamental building block of silicate minerals consisting of four oxygen ions that are covalently boonded to one comparatively small silicon ion They re complex ions having a net charge of 4 and bond to positively charged metal ion leaving the 1 charge left over because the 02 ions bond to the 54 ions in the middle to bond with another positive ion or a silicate in another tetrahedral Minerals with Independent Tetrahedra Consist of independent siliconoxygen tetrahedrons with the 01 ions bonding to a positive ion such as Mg2 Fe2 and Ca2 Eg olivine bonds siliconoxygen tetrahedrons to Mg and Fe ions Minerals with Chain or Sheet Structures Silicate tetrahedral can link to one another in a variety of con gurations a phenomenon called polymerization achieved by the sharing of 14 oxygen atoms with adjacent tetrahedra Minerals with Three Dimensional Frameworks All four oxygen ions are shared As more oxygen ions are shared the percentage of silicon in the structure increases Silicates are grouped in high and low silicon content three dimensional structures having the highest and independent tetrahedra having the lowest Joining Silicate Structures Other than quartz the basic structure of most silicate minerals have net negative charges and must bond to positive metallic ions iron magnesium potassium sodium aluminum and calcium Hybrid bonds between silicon and oxygen are stronger than ionic bonds that hold one silicate structure to the next which creates cleavage and sometimes hardness properties Because most silicate structures will accommodated two or more different positive metal ions at a given bonding site as a result many silicate minerals contain varying amounts of certain elements and even minerals in a mineral group have ranges of compositions between two members 39 Common Silicate Minerals Chart Olivine Group 0 Magnesium iron 0 No cleavage 0 Single tetrahedra Pyroxene Group 0 Magnesium Iron 0 Cleavage at two planes 909 0 Single chains Amphibole Group hornblende 0 Calcium lron Magnesium Hydrogen o Cleavage at two planes 60 and 909 0 Double chains Biotite mica 0 Potassium magnesium iron aluminum hydrogen o Cleavage on one plane 0 Sheet Muscovite mica 0 Potassium aluminum hydrogen 0 Cleavage on one plane 0 Sheet Potassium Feldspar orthoclase 0 Potassium aluminum 0 Cleavage at two planes 909 0 Three dimensional Plagioclase feldspar 0 Calcium sodium aluminum 0 Cleavage at two planes at 909 0 Three dimensional Qua z 0 Silicon oxygen on o No cleavage 0 Three dimensional Most silicate minerals form when molten rock cools and crystallizes and its chemical composition indicates the environment it crystallizes in Light Silicates 0 Light or nonferromagnesian silicates are generally light in color and have a speci c gravity of 27 with attribute to the absence of iron and magnesium 0 Contain various amount of aluminum potassium calcium and sodium Feldspar Group 0 Can form under a range of temperatures and pressures Two groups potassium feldspar orthoclase and plagioclase Striations are found on some cleavage planes on plagioclase but not on potassium feldspar Qua z o The only common silicate mineral consisting only of silicon and oxygen which is why its called silica Three dimensional structure is created by strong hybrid bonds between silicon and oxygen and creates its hardness resistance to weathering and no cleavage Muscovite o Mica family light in color with a pearly luster o In the thin sheets muscovite is clear and shiny identi ed by the sparkle it gives a rock Clay Minerals 0 Category of complex minerals that have sheet structure but originiate as products of chemical breakdownweathering of other silicate minerals Make up a large percentage of soil agricultural importance and supporting materials for buildings 0 Fine grained texture makes identi cation dif cult Layered structure and weak bonding gives them a wet characteristic 0 Kaoliniteis used in manufacture of ne china andn as coting for higgloss paper Dark Silicates Dark or ferromagnesian silicates are minerals containing iron and or magnesium ions in their structure 0 They are dark in color with a larger speci c gravity between 32 and 25 Olivines pyroxenes amphiboles dark mica biotite and garnet Olivine Group 0 Hightemperature silicate minerals that are black to olive green in color with glassy luster and conchoidal fracture Form small round crystals that give a granular appearance 0 Common in basalt and thought to constitute up to 50 of mantle Pyroxene Group 0 Diverse minerals that are important components in ddarked colored igneous rocks 0 Augite is one of the dominant minerals inbasalt a common igneous rock of the oceanic crust and volcanic areas on continents Amphibole Group Hornebleand is the most common which is usually dark green and except for 60 and 1209 cleavage appears very similar to augte 0 Forms elongated crystals 0 Found in igneous rock where it makes up the dark portionof an often light colored rock Biotite Dark iron rich mica with shiny black appearance Common constitute of igneous rocks granite Garnet Individual tetrahedra linked by metallic ions glassy luster lacks cleavage and conchoidal fracture like olivine Brown to deep red often times Well developed crystals have 12 diamondshaped faces and are commonly found in metamorphic rocks 310 Important Nonsilicate Minerals Common nonsilicate minerals belong to carbonate sulfate and halide groups Carbonate is composed of carbon and oxygen ions 0 Calcite calcium carbon oxygen 0 Dolomite Calcium magnesium carbon oxygen Halite sodium choride and gypsum calcium sulfur oxygen hydrogen are found in sedimentary rocks in thick layers that are the last vestiges of ancient sease o Halite used for salt gypsum used for plaster Important economic value 0 Hematite and magnetite are important iron ores o Galena lead sphalerite zinc and chalcopyrite copper 0 Gold silver and diamonds o Fluorite ux in making steel corundum gemstone abrasive and uraninite uranium source 9415 Lecture Notes Recap from Tuesday The way atoms bond depends on the electron farthest from the Nucleus Atoms want nal energy level to be 1 full or completely empty meaning the lower level is full 2 exactly 12 full Atoms gain or lose electrons to get a more stable energy level After NaCl trades electrons Na gives Cl an electron they both become ions or charged atoms Na who loses and electron becomes a cation a positively charged ion Cl who gains an electron becomes an anion a negatively charged ion By forming an IONIC BOND they become NaCl the mineral salt halite Minerals There are over 4000 different minerals but only 12 are the main ones that make up the Earth called common rockforming minerals 1 rock is made of one or more minerals Of the dozen minerals only about 8 elements are needed to make them and they make up most of the terrestrial planets which aren t made out of gas SILICON Si OXYGEN O ALUMINUM Al IRON Fe MAGNESIUM Mg CALCIUM Ca SODIUM Na POTASSIUM K Ignoring the curs the Earth is made ofjust Si 0 Fe and Mg A mineral MUST be A solid Naturally occurring Inorganic usually Crystalline There are different quotclansquotgroups of minerals and what each clan has in common are the atoms that join the cation The most important clan is the SILICATES SiO which make up most of the planet silicon and oxygen The other groups we need to know are HALIDES Cl like NaCl and KCI SULFIDES S mostly sul de minerals like Galena PbS Sphalerite ZnS Pyrite FeS aka fools gold good for building things SULFATES SO4 Gypsum CaSO4 used to make drywall CARBONATES CO3 like Calcite CaCO3 that makes up limestone that zzes and dissolves in dilute acid Silicates Silicates make up the most of Earth s crust and mantle thus the most important by volume The building block is 4 bis oxygen anions negative surrounding little silicon cation Silica Tetrahedron sort of a pyramid shape with single cation in the center and 4 oxygen anions surrounding it 3 at the base one at the tip Nesosilicate Clan is a SUBCLAN with 8 independent islands of silica tetrahedron with positive oxygen ions connecting them all Olivine Mineral aka part of the mantel Unshared tetrahedral XnSilO4 in a chain with unshared oxygen Pyroxene group of minerals Tetrahedra can joini nto chains where oxygen ions are shared Amphibole group of minerals join or polymerize two chains together and get a double chain with increased sharing of tetrahedral edges Mica group of minerals join or polymerize two chains together to get a double chain with to get a sheet structure There s an even more complex way of combining the simple silica tetrahedron and make something as simple as quartz Si02 How do these silicate minerals form Need to look at MAGMA Different minerals crystalize at different temperatures and under different chemical conditions AN ELEMENT IS NOT A MINERAL WHICH IS NOT A ROCK these are simply parts of parts of rocks 9815 Lecture Notes Silicon Tetrahedron The building block of all silicate minerals 4 oxygen ions surround on Si ion How do silicate minerals form We look at MAGMA Different minerals crystallize at different temperatures and under different chemical conditions from very hot liquids As the silicate liquid thousands of degrees hot cools off tiny crystals start to grow until there is a network of intergrown crystals and all the magma is used up Magma is very viscous not as liquid as water Different minerals crystallize at different temperatures from magma viscous liquid gt 700 degrees 2 main groups of SILICATE minerals crystallize from magma 1 FeMg Rich dark greenalmost black a Olivine pyroxene hornblende and other amphibole minerals biotite 2 FeMg Poor generally lighter colors a Quarts Potassium Feldspar orthoclase found in the Earth s crust Calcium feldspar plagioclase Muscovite K rich form of mica What is the Crystallization Order of Minerals We ask quotwhich minerals melt first but we should really ask quotwhich have the lowest melting pointquot Remember meltingcrystallizing is like meltingfreezing BOWENS REACTION Crystallization order from 1st to last from high temp to low Olivine 1200 C Pyroxene Amphibole Biotite K Feldspar Muscovite Quartz 600 C THEREFORE we would expect to nd certain minerals together the ones with similar crystallization temperatures So olivine pyroxene and Carich plagioclase together make sense Amphibole biotite and intermediate plagioclase together make sense K feldspar muscovite quartz together make sense Think about mineral groupings when thinking about rocks Mineral Identi cation Basics Internal crystal structure Minerals results of atoms joining together via electrical bonds producing speci c internal structure It s the nature of the atoms and the strength of the chemical bonds that determine many of the minerals physical and chemical properties Physical properties hardness Being hard is being more SCRATCH RESISTENT If you rub quartz crystal across a glass plate the glass plate will be scratched therefore the quartz crystal will be harder Moh s scale of mineral hardness from soft to hard Talc Gypsum Calcite Fluorite Apatite bones and teeth Orthoclase Qua z Topaz Corundum rubies and sapphires 10 Diamond The GirlsGuys Can Flirt And Other Quaint Things Can Do The hardness of common items Fingernails 25 Copper Penny 3 Glass 55 Steel File 665 DPOFP P FWN Physical Properties cleavage Within this crystalline pattern you can see how atoms will separate to produce cleavage with 90 degree angles It s similar to tearing a piece of paper that has perforations in it The paper will tear along the perforations they are zones of weakness Mica has perfect cleavage in ONE direction breaks into sheets Fluorite has cleavage in 4 directions breaks into cubes Common salt halite has very good cleavage in 3 directions cubic cleavage so when you put salt under a microscope it looks like small cubes Physical Properties fracture Quartz crystal was struck with a hammer to show the external form of crystal that does not repeat when broken This is a good example of conchoidal fracture similar to glass bottles Physical Properties streak Streak is de ned as the color of the mineral in powder form more accurate than regular color Streak is normally obtained by rubbing a mineral across a quotstreak platequot The powder color is the streak Hematite is a reddish brown streak Sphalerite is a dark mineral with a light colored streak Next to hematite the powder is a light yellow Physical Properties Color The color of a mineral not is streak is the rst thing one may notice about a mineral Sadly it is normally NOT a great physical property to rely one A lot of minerals have different color variations but the same makeup Quartz comes in a large amount of variations because it is heavily affected by the tiniest impurities Indicative color some minerals do have certain color associated with them Some examples are Turquoise which is the same color as its name malachite oxidized copper green rhodochrosite pink azurite azure blue and sulfur bright yellow Physical Properties speci c gravitydensity Weighing the specimen on the air and then weighing it in the water determine speci c gravity of a mineral Speci c Gravity weight in air weight in airweight in water Speci c Gravity of some Minerals Halite 22 Orthoclase 26 Quartz 27 Biotite 30 Apatite 32 Zircon 45 Pyrite 50 FP P PP N The Rock Cycle Rocks are naturally occurring combinations of minerals They are classi ed by the way in which they form The three rock types igneous sedimentary and metamorphic Igneous rocks are quotborn of requot they were once molten and upon cooling the magma molten rock crystallized into solid rock They can form deep in the earth or at the surface after a volcano Intrusive plutonic Igneous rocks Slow cooling deep beneath the Earth s surface allows crystals to slowly grow to large size several millimeters or bigger These crystals are easily visible 91014 Lecture Notes Rocks and How to Identify Them Rocks are naturally occurring combinations of coherent aggregates of minerals They are classi ed by the way in which they form 0 The three rock types are igneous sedimentary and metamorphic Igneous Rocks 0 are quotborn of firequot In other words they were once molten and upon cooling the magma molten rock crystallized into solid rock 0 They may form deep inside the Earth or at the Earth s surface eg when a volcano erupts Intrusive or Plutonic Rocks Slow cooling igneous rocks deep beneath the Earth s surface allow crystals to slowly grow to large size several millimeters or bigger These crystals are easily visible Extrusive rocks Rapid cooling nere or at the earths surface produces small crystals hard to see to the naked eye These rocks are volcanic in origin Cooling may be so rapid that no crystals have the chance to form instead volcanic glass is produced Rocks formed by slow cooling followed by rapid cooling are porphyritic rocks Igneous rocks are classi ed by 1 Texture 2a Mineral Types and amounts 2b Chemical composition 0 Very different looing igneous rocks might be equivalents in terms of chemical composition 0 Comparison of felsic and ma c igneous rocks 0 Felsic rocks composed of feldspar and are silica rich Typical minerals are quartz Kfeldspar plagioclase minerals made up of K Al Ca and of course Si 0 Ma c rocks composed of magnesium and Fe rich minerals pyroxene olivine plagioclase little to no quartz and Kfeldspar Granite intrusive Granite is a coarse to mediumgrained rock that forms from cooling of magma deep within the Earth 0 It s made up of quartz Kfeldspar and plagioclase It usually also contains biotite or sometimes muscovite or hornblende Rhyolite extrusive o Rhyolite is a negrained rock that forms near the surface of the Earth rapid cooling o It is also made up of quartz Kfeldspar and plagioclase It also often contains biotite But these are so small that it can be hard to see them 0 The name comes from the Greek rhyax quotstream of lavaquot o Rhyolite is very viscous and thus ows very slowly lt cools quickly so only microscopic sized crystals develoo The volcanoes that produce rhyolite are very explosive varieties like Mt St Helens Krakatoa and Vesuvius 0 Frequently it is banded due to ow alignment of different minerals Gabbro intrusive Gabbro is a coursegrained rock that is high in iron and magnesiumbearing minerals pyroxene and olivine and Carich feldspar plagioclase The rock is dark denser than granite and has NO quartz It s so dark it s almost black Sometimes people call very dark gabbro quotblack granitequot even though there is no such thing as black granite Basalt extrusive Basalt is the extrusive equivalent to Gabbro it is difficult to see the minerals without a microscope o It is also high in iron and magnesium bearing minerals pyroxene and olivine and calciumrich feldspar plagioclase The holes in basalt are called vesicles air bubblesnatural gases escapes from the lava and makes the holes Diorite intermediate intrusive o Diorite is similar to granitic rocks but is distinguished by the absence of visible quartz Generally it has a salt and pepper appearance 12 biotite black and 12 feldspar white Read about andesite equivalent to diorite dacite equivalent to tonalite and rhyodacite equivalent of granodiorite in the text Igneous rocks Intrusive Extrusive Granite Rhyolite Granodiorite Rhyodacite Tonalite Dacite Diorite Andesite Basalt Gabbro Ultra ma c Rocks intrusive Dunite is composed of gt 90 olivine As a result it is characteristically apple green This material is thought to make up the very top of the Earth s mantle Peridotite is composed of a mix of olivine and pyroxene thus black and applegreen minerals This material is thought to make up almost all of the Earth s mantle Special Cases Pegmatite is classi ed as an intrusive igneous rock but there is a difference They are VERY course grained st sized crystals The coarse grained nature is a result of crystal growth in aqueous solutions related to the end of magma crystallization How do rocks melt Solidus the minimum temperature where a rock or a region of the crust just begins to melt 0 Only low melting point minerals will rst melt 0 Melt will be different composition that source rock Liquidus the temperature reached where a rock is totally melted is called the liquidus temperature 0 Melt will be the same composition as source rock How do rocks melt 1 Heating obvious but not most important cause of melting
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