Physical Science (Geology)
Physical Science (Geology) GS 106
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MINERALS Minerals must Be naturally occurring Be inorganic Be solid Have an orderly internal structure Have a de nite chemical composition Gold Mineral vs Nonmineral Periodic Table of the Elements Lanthamde 39 Se es vActxmde 3910 series ATOMIC BONDING BOND Forms a compound with 2 or more elements Attaching of atoms together BOND TYPES IONIC BOND COVALENT BOND METALLIC BOND ATOMIC BONDING IONIC BOND Atoms give up gain valence electrons to form ions ANION Negatively charged due to a gain of an electrons CATION Positively charged due to a loss of an electrons EXAMPLE NaCl ATOMIC BONDING COVALENT BOND Atoms share electrons Gaseous elements EXAMPLES H2 02 nghspeed Nucleus electrons 7 7 i 7 1ncarye x k r quot r r my 7 Atom Neutrons charge no charge Structure Third energylevel shell Second energylevel shelll Flrst energyAle39vel shell Properties Crystal Form Luster Color Streak Hardness Cleavage Fracture DensitySpecific Gravity Crystal Form Crystal Form Crystal Form Luster def Sem b PHYSICAL PROPERTIES MINERAL STREAK Color of mineral in its powdered form Helps to distinguish metallic luster PHYSICAL PROPERTIES HARDNESS Hardness of Some Common Objects Diamond quot39 QCorundum 8Topaz 7 Quartz GOrthoclase Feldspar 5 Apatite 39 30alcite 2Gypsum 1 Talc Table 22 Mohs scale of mineral hardness Hardness of Some Relative Scale Mineral Common Objects 55 Glass Masonry nail 45 Wire iron nail 35 Copper wire or coin penny 25 Fingernail Hardest 10 Diamond Corimdum Topaz Quartz Potassium 55 Glass Pocketkm39fe feldspar 5 Apatite 4 Fluorite 3 Calcite 3 Copper penny 2 1 310059 Gypsum 25 Fingernail Softest Talc PHYSICAL PROPERTIES MINERAL CLEAVAGE Cleavage in Aquot Micas biotite n m 39 one direction d UUUU We Cleavage in Orthoclas two directions at right angles Cleavage in three directions Halite galena at right angles Cleavage i three direct n Calcite ot at right dolomite angles Clem619 Fluorite four directions diamond Sphalerite PHYSICAL PROPERTIES C Hornblende an arnphibole has two good directions of cleavage at 124 from each other The irregular darkest surface is a fracture not cleavage D Galena has three good directions of cleavage that form two 90 angles in two perpendicular planes This type of cleavage called cubic produces a form with six sides Recall halite ineral Cleavage E Calcite exhibits three good directions of cleavage that form angles of 105 in one plane and 750 in another This rhombohedral or rhombic cleavage 39 produces a form with six sides that slants toward one of its corners A Biotite and muscovite micas exhibit one excellent direction of cleavage allowing these minerals to be peeled like an onion F Fluorite has four good directions of cleavage This type of cleavage called octahedral produces a form with eight sides B Orthoclase and plagioclase feldspars exhibit two good directions of cleavage at approximately 90 from each other The irregular darkest surface is a fracture not cleavage PHYSICAL PROPERTIES MINERAL CLEAVAGE PHYSICAL PROPERTIES FRACTURE Absence of cleavage when broken Types of fracture irregular and conchoidal 7 l is 1 3 7 3 I r r r in Silicates Most abundant type of mineral Contains silica 2 groups light and dark Dark has iron and magnesium dense Light has lighter density color Emile K39WEFHJENEWJUHE GEOLOGIC TIME DIVISIONS OF THE TIME SCALE 1 Law of Superposition ldest rocks on the bottom ounger rocks on the top Principle of Horizontality Layers are generally eposited horizontally Flat rock layers have not een disturbed 3 Principle of Crosscutting Relationships Younger feature cuts through an older feature 4 Inclusions ne rock unit is enclosed Within another The rock containing the inclusions is younger than the inclusions x Fault B Interpretation 1 Applying the law or superposition heels A E C and E were deposited Iquot ma emu V 5 Beds SJt l J and K were the prlndpl H a mung 39 r quotr deposited In Ihal order again D elmon s e V r39 Iquot 1 deare e usfons in the sill o lragmems mm mesa beds ll mks igneous mass 7 contalns pieces of adaoant strata than lbs adjacent slrala must have been than lint l I 39 39 4 Next the rocks were lllled and eroded ha pence u 3 Following the lnlmslon of sill D quotEd The mung 7 I118 upturned an the inlvusvon of dlks F menu quot3 ds a ha tmla have Because the dlke cuts edge youn r than 133an mlhzllple 39 men 9mg T29 N amm39 2 r owed un er deposition og msscunm mumsmml 39 V produced an angular unconformlm mrrvn DATING FOSSIL SUCCESSION Fossils the remains or traces of prehistoric life Fossil Types Relatively recent organisms Entire animals esh included Petri ed turned to stone Molds and Casts Carbonization Others tracks burrows coprolites gastroliths LATIWE DATING FOSSIL SUCCESSION Conditions favoring preservation Rapid burial and possession of hard parts CORRELATION OF ROCK LAYERS Matching rocks of similar age Fossils succeed one another in a de nite order Index Fossils widespread and shortlived Fossils are environmental indicators land or sea Age ranggslansmerfossii groups l A Younger TIME Older Copyright 2006 Pearson Prentice Hall Inc ABSOLUTE DATING BASIC ATOMIC STRUCTURE Protons Neutrons and Electrons Atomic number of protons Mass number of protons of neutrons Isotope same of p s different of n s ABSOLUTE DATING RADIOACTIVITY Spontaneous breaking apart decay of atomic nuclei TYPES OF RADIOACTIVITY Alpha Emission Beta Emission Electron Capture ABSOLUTE DATING RADIOACTIVITY The of radioactive atoms that decay during one halflife is always the same 50 The actual of atoms that decay during one Halflife continually decreases Comparing the ratio of parent to daughter isotopes yields the age of the sample ABSOLUTE DATING RADIOACTIVITY Rubidium87 Strontium 87 Thorium232 Lead208 Uranium 238 Lead206 Uranium235 Lead208 Potassium40 Argon40 Closed system is required Unweathered samples are used to avoid contamination ABSOLUTE DATING RADIOACTIVITY KAr Dating Millions of years RbSr Dating Billions of years ABSOLUTE DATING RADIOACTIVITY Carbonl4 Dating Only has a halflife of 5730 yrs Only useful for recent samples DIVISIONS OF THE GEOLOGIC TIME SCALE Subdivides geologic history into units Originally created using relative dates Structure of the geologic time scale Eons Eras Periods lipochs GEOIL OGIC TIME SCALE GEOLOGIC TIME SCALE 4600 my CENOZOIC my 2500 my GEOLOGIC TIME SCALE EONS Precambrian and Phanerozoic Precambrian Eon ERAS Hadean Archaen Proterozoic Phanerozoic Eon ERAS Paleozoic Mesozoic Cenozoic GEOLOGIC TIME SCALE ERAS OF THE PHANEROZOIC ARE SPLIT INTO PERIODS Paleozoic Era ancient life Periods Cambrian Ordivician Silurian Devonian Mississippian Pennsylvanian Permian Mesozoic Era middle life Periods Triassic jurassic Cretaceous Cenozoic Era recent life Periods Tertiary Quaternary GEOLOGIC TIME SCALE TERTIARY ANDQUATERNARY PERIODS ARE SPLIT INTO EPOCHS Tertiary Period Paleocene eocene Oligocene Miocene Pliocene EPOC HS Quaternary Period Holocene and Pleistocene EPOC HS GEOLOGIC TIIVIE SCALE PNEUMONICS Come Over Some Day Maybe Play Poker Three Jacks Cover Two Queens Can Old Senators Demand More Political Power Than Junior Congressmen Tough Question Earth s external processes Earth s external processes 0 Weathering the physical breakdown diSintegl ation and Chemical alteration Erosion the physical removal of material decomPOSItlon 0f Wk at 01 near Earth s by mobile agents such as water wind ice or surface gravity 0 Mass wasting the transfer of rock and soil downslope under the influence of gravity Weathering Frost wedging Frost wedging 0 Two types of weathering Mechanical weathering breaking of rocks into smaller pieces Four types of mechanical weathering 7 Frost wedging alternate freezing and thawing of water in fractures and cracks promotes the disintegration of rocks Exfoliation of igneous rocks Weathering Mechanical Weathering continued 7 Unloading exfoliation of igneous and metamorphic rocks at the Earth s surface due to a reduction in confining pressure 7 Thermal expansion alternate expansion and contraction due to heating and cooling 7 Biological activity disintegration resulting from plants and animals J 39 i l r Uplift and I 39 erosion Weatherlng Chemical Weathering Breaks down rock components and the internal structures of minerals 0 Most important agent involved in chemical weathering is water responsible for transport of ions and molecules involved in chemical processes Weathering Major processes of chemical weathering Dissolution 7 Aided by Slnall amounts of acid in the water 7 Soluble ions are retained in the underground water supply 0 Oxidation 7 Any chemical reaction in which a compound or radical loses electrons Weathering Major processes of chemical weathering Oxidation continued 7 r I A A in I D lninerals Hydrolysis 7 The reaction of any substance with water 7 Hydrogen ion attacks and replaces other positive lons Table 51 Products of weathering Residual Material Mineral Products in Solution Quartz Quartz grains Silica Feldspars Clay minerals Silica K Na Ca2 Amphibole Clay minerals Silica Ca2 Mg2 hornblende Limonite Hematite Olivine Limonite Silica Mg2 Hematite Weathering Alterations caused by chemical weathering Decomposition of unstable minerals 0 Generation or retention of materials that are stable 0 Physical changes such as the rounding of corners or edges Weathering Rates of weathering 0 Advanced mechanical weathering aids chemical weathering by increasing the surface area Others factors affecting weathering 0 Rock characteristics 7 Rocks containing calcite lnarble and linlestone readily dissolve in weakly acidic solutions Increase in surface area by mechanical weathering Weath ermg Others factors affecting weathering Rock characteristics continued Silicate minerals weather in the same order as their order of crystallization Climate Temperature and moisture are the most crucial 4 square units x 1 square unit X 25 square unit I faCtorS 6 sides X 6 sides X 6 sides gtlt o o o o L W m Chemical weathering is most effective in areas of 24 square units 48 square units 96 square units warm moist climates Jointcontrolled weathering in ign e0 as rocks Weathering 0 Differential weathering Masses of rock do not weather uniformly due to regional and local factors Results in many unusual and spectacular rock formations and landforms Soil Soil Soil is a combination of mineral and organic 0 Factors controlling soil formation mater water and air Parent material 39 That portion of the regolith rock and Residual soil parent material is the underlying mineral fragments produced by weathering bedka that supports the growth of plants Transported soil forms in place on parent material that has been carried from elsewhere and deposited Soil 0 Factors controlling soil formation 0 Time Important in all geologic processes Amount of time for soil formation varies for different soils depending on geologic and climatic conditions Climate Most in uential control of soil formation Key factors are temperature and precipitation Soil 0 Factors controlling soil formation 0 Plants and animals Organisms in uence the soil s physical and chemical properties Also furnish organic matter to the soil Slope Steep slopes often have poorly developed soils Optimum terrain is a attoundulating upland surface Variations in soil development due to topography N0 soil developmenl V because of very steep slope T39anSPO EC 50quot 395 t developed on unconsolldaled deposlls Residual soil is developed on bedrock Bedrogk Thmner SDII on slope 7 because dl erosion Unconsolldaled deposits 39 Soil 0 The soil profile Soil forming processes operate from the surface downward Vertical differences are called horizons zones or layers of soil An idealized soil pro le 0 honzon Loose and vanly decayed orgamc mailer Topsoil A horizon Mineral mauer Mixed wlm some humus Solurn or me souquot E holrzon nghl colored mineral particles Zone 039 eluvvallon and leaemng E hanmn Accumulahon at ll sub clay transponed lmm above c horizon Partially altered pavonl matanul Unwealhered parenl material A soil pro le sh owing different horizons Soil I Soil erosion I Recycling of Earth materials I Natural rates of soil erosion depend on 7 Soil characteristics 7 Type of vegemtion Soil I Soil erosion I In many regions the rate of soil erosion is significantly greater than the rate of soil I Sedimentation and chemical pollution 7 Related to excessive soil erosion 7 Occasionally soil particles are contaminated with pesticides What is a sedimentary rock I Sedimentary rocks are products of mechanical and chemical weathering I They account for about 5 percent by volume of Earth s outer 10 miles I They contain evidence of past environ I Provide information about sediment transport I Often contain fossils Turning sediment into rock I Many changes occur to sediment after it is deposited I Diagenesis all of the chemical physical and biological changes that take place after sediments are deposited I Occurs within the upper few kilometers of Earth s crust Turning sediment into rock I Diagenesis I Includes 7 Recrystallization 7 development of more stable minerals from less stable ones 7 Iithi cation 7unconsolidated sediments are transformed into solid sedimentary rock by gtgt Compaction gtgt Cementation by calcite silica and iron oxide Types of sedimentary rocks I Sediment originates from mechanical andor chemical weathering I Rock types are based on the source of the material I Detrital rocks transported sediment as solid partic es I Chemical rocks sediment that was once in solution D etr Ital sedlm en quot3 rOCks Table 61 Particle size classification for detrital rocks The chief constituents of detrital rocks Common indllde Size Range Particle Sediment Detrital Clay minerals millimeters Name Name Rock 39 Quartz gt256 Boulder Feldspars 64 256 Cobble Gravel Conglomerate Micas 4 64 Pebble or breccia 0 Particle size is used to distinguish among 2394 Granule the various t es of detrital rocks 16 2 sand sand sandsmne yp 1256 116 Silt M d Shale or lt 1 256 Clay u mudstone Sh ale containing plant remains Detrital sedlm entaly rocks 0 Common detrital sedimentary rocks in order of increasing particle size Shale 7 Mudsized particles in thin layers that are commonly referred to as laminea 7 Most common sedimentary rock uart sandstone Detrital sedimentary rocks Q z Sandstone 7 Composed of sandsized particles 7 Forms in a variety of environments 7 Sorting shape and composition of the grains can be used to interpret the rock s history 7 Quartz is the predominant mineral Detrital sedimentary rocks congIOmeml e Conglomerate and breccia 7 Both are composed of particles greater than 2mm in diameter 7 Conglomerate consists largely of rounded gravels 7 Breccia is composed mainly of large angular particles Breccia Chemical sedimentary rocks 0 Consist of precipitated material that was once in solution Precipitation of material occurs in two ways Inorganic processes Organic processes biochemical origin Coquina Chemical sedimentary rocks 0 Common chemical sedimentary rocks Limestone 7 Most abundant chemical rock 7 Composed chie y of the mineral calcite 7 Marine biochemical limestones form as coral reefs coquina broken shells and chalk microscopic organisms 7 Inorganic limestones include travertine and oolitic limestone F ossiliferoas limestone v Chemical sedimentary rocks 0 Common chemical sedimentary rocks Dolostone 7 Typically formed secondarily from limestone Chert 7 Made of microcrystalline quartz 7 Varieties include int and jasper banded form is called agate Rock salt Chemical sedimentary rocks ff i 0 Common chemical sedimentary rocks 3 Evaporites 7 Evaporation triggers deposition of chemical precipitates 7 Examples include rock salt and rock gypsum Chemical sedimentary rocks 670551170 th 0f 0 Common chemical sedimentary rocks sedlmentary VOCkS Coal Sedimenta rocks are classified ac 7 Different from other rocks because it is ry composed of organic material cording to the type of material 7 Stages in coal formation in order 0 TWO major groups 1 Plant material Detrita 2 P t fa Chemlcal 3 ngmte 4 Bituminous Classification of sedimentary rocks 0 Two major textures are used in the Table 62 Classification of sedimentary rocks Sediment Name Texture and Particle Size Gravel gt2 mm DETRl l AL ROCKS Comments Rounded rock fragments Angular rotk fragments Quartz predominates Rotk Name Conglomerate BH CCld Quartz sandstone Claskic Sand 1 16 2 mm Quartr with uonsiderable feldspar Arkose Dark color quartz with cmwclerable 1 class1f1catlon of sedimentary rocks WWWanalMomma Mud til 16 mm Splits into thin layers Shale C Breaks into clumps or blocks Mudslone CHEMICAL ROCKS Discrete fragments and particles Group Texture Composition Rack Name Clastic or nonclastic Calcite 1100 Limestone All detrital rocks have a clastic texture Nundastic Dolomite CinMgCO J Dolosione hmrg nic Nondastic Micmcrvstalline quart QiO Clmrt D I x p s OHClaStlc Nonclastic llnlite NaCl Rock salt P e rn 0f erlo cking crystals Nondas tic Gypsum C5150 ZHEO Rock gypsum Clashc or nnnclastic Calcite CaCD3 Limestone May resem ble an igneous rock Biochemica Nondnstic Micrucwstalline quartz 53910 Chert NOl39IdPISIiC Altered plant 1 1139I39Il1 5 lCoal Sedimentary environments Sedimentary environments 0 A geographic setting Where sediment is Types Of sedimentary environments Continental accumulating Dominated b erosion and de osition associated Determines the nature of the sed1ments that with streamsy p accumulate grain size grain shape etc Glacial Wind eolian Marine Shallow to about 200 meters Deep seaward of continental shelves Continental left and marine right depositional environments Nonmetalllc mineral resources s 0 Use of the word mineral is very broad 9 73 is Sand dunes I 7 Two common groups Building materials Natural aggregate crushed stone sand and gravel Gypsum plaster and wallboard Clay tile bricks and cement I R eef Barrier island Table 63 Uses of nonmetallic minerals Mineral Uses petite Phosphorus fertilizers Asbcitos chrysotilc inmmbus blc bers Calcite Aggregate steelmaking soil conditioning hemir cals Cemenl building stone Clay minerals kanljnite Ceranlics china Comndum Garnstoncs abrasivus Dianxond Gemston 39 uorite Garnet Abrasives gemstones Graphite Pencil 153d lubricant refractories Gypsuxn Plaster of Paris Halite Table salt chemicals ice comm Muscov ile Insulator in electrical applicaLions Quartz rimary ingredient in glass Sulfur Chemicals fertilizer manufacture Sylvire Potassium fertilizeis Talc w er used in palntlt cosmetics etc Energy resources from sedimentary rocks Coal Formed mostly from plant material Along with oil and natural gas coal is commonly called a fossil fuel The major fuel used in power plants to generate electricity Potential environmental problems from mining and air pollution Subbilum mnus coal 95m BinII Lignila 6700 Btulb Energy resources from sedimentary rocks Oil and natural gas 397 Derived from the remains of marine plants and animals Both are composed of various hydro carbon compounds and found in similar environments Oil trap geologic environment that allows significant amounts of oil and gas to accumulate Energy resources from sedimentary rocks Oil and natural gas Two basic conditions for an oil trap 7 Porous permeable reservoir rock 7 hnperineable cap rock such as shale a Cap rock keeps the mobile oil and gas from escaping at the surface 1O Minerals Building Blocks of Rocks Minerals Building Blocks of Rocks begins with an explanation of the difference between a mineral and a rock followed by a formal de nition of a mineral Elements atoms compounds ions and atomic bonding are explained Also investigated are isotopes and radioactivity Following descriptions of the properties used in mineral identi cation the silicate and nonsilicate mineral groups are examined The chapter concludes with a discussion of mineral resources reserves and ores Learning Objectives After reading studying and discussing the chapter students should be able to Explain the difference between a mineral and a rock Describe the basic structure of an atom and explain how atoms combine List the most important elements that compose Earth s continental crust Explain isotopes and radioactive decay Describe the physical properties of minerals and how they can be used for mineral identi cation List the basic compositions and structures of the silicate minerals List the economic use of some nonsilicate minerals Distinguish between mineral resources reserves and ores Ch apter Summary 0 A mineral is a naturally occurring inorganic solid that possesses a de nite chemical composition and a de nitive molecular structure that gives it a unique set of physical properties Most rocks are aggregates composed of two or more minerals o The building blocks of minerals are elements An atom is the smallest particle of matter that still retains the characteristics of an element Each atom has a nucleus which contains protons particles with positive electrical charges and neutrons particles with neutral electrical charges Orbiting the nucleus of an atom in regions called energy levels or shells are electrons which have negative electrical charges The number of protons in an atom s nucleus determines its atomic number and the name of the element An element is a large collection of electrically neutral atoms all having the same atomic number 0 Atoms combine with each other to form more complex substances called compounds Atoms bond together by gaining losing or sharing electrons with other atoms In ionic bonding one or more electrons are transferred from one atom to another giving the atoms a net positive or negative charge The resulting electrically charged atoms are called ions Ionic compounds consist of oppositely charged ions assembled in a regular crystalline structure that allows for the maximum attraction of ions given their sizes Another type of ond the covalent bond is produced when atoms share electrons o Isotopes are variants of the same element but with a different mass number the total number of neutrons plus protons found in an atom s nucleus Some isotopes are unstable and disintegrate naturally through a process called radioactivity ll 12 CHAPTER 2 o The properties of minerals include crystal form luster color streak hardness cleavage fracture and speci c gravity In addition a number of special physical and chemical properties taste smell elasticity malleability feel magnetism double refraction and chemical reaction to hydrochloric acid are useful in identifying certain minerals Each mineral has a unique set of properties that can be used for identi cation 0 Of the nearly 4000 minerals no more than a few dozen make up most of the rocks of Earth s crust and as such are classi ed as rock forming minerals Eight elements oxygen silicon aluminum iron calcium sodium potassium and magnesium make up the bulk of these minerals and represent over 98 percent by weight of Earth s continental crust o The most common mineral group is the silicates All silicate minerals have the negatively charged silicon oxygen tetrahedron as their fundamental building block In some silicate minerals the tetrahedra are joined in chains the pyroxene and amphibole groups in others the tetrahedra are arranged into sheets the micas biotite and muscovite or threedimensional networks the feldspars and quartz The tetrahedra and various silicate structures are often bonded together by the positive ions of iron magnesium potassium sodium aluminum and calcium Each silicate mineral has a structure and a chemical composition that indicates the conditions under which it formed 0 The nonsilicate mineral groups which contain several economically important minerals include the oxides eg the mineral hematite mined for iron sul des eg the mineral sphalerite mined for zinc and the mineral galena mined for lead sulfates halides and native elements eg gold and silver The more common nonsilicate rockforming minerals include the carbonate minerals calcite and dolomite Two other nonsilicate minerals frequently found in sedimentary rocks are halite and gypsum 0 Mineral resources are the endowment of useful minerals ultimately available commercially Resources include already identi ed deposits from which minerals can be eXtracted pro tably called reserves as well as known deposits that are not yet economically or technologically recoverable Deposits inferred to eXist but not yet discovered are also considered as mineral resources The term ore is used to denote those useful metallic minerals that can be mined for a pro t as well as some nonmetallic minerals such as uorite and sulfur that contain useful substances Chapter Outline 1 Minerals The building blocks of rocks B Atoms A Mineral de nition 1 Smallest particles of matter 1 Naturally occurring 2 Retains all the characteristics of an 2 Inorganic element 3 Solid C Atomic structure 5 Orderly internal structure 1 Nucleus which contains 4 De nite chemical structure a Protons positive electrical B Rock a solid natural mass of mineral char es or minerallike matter b Neutrons neutral electrical charges 11 Composition of minerals 2 Electrons A Elements a Surround nucleus 1 Basic building blocks of minerals b Negatively charged zones called 2 Over 100 are known 92 naturally energy levels or shells occurring Minerals Building Blocks of Rocks 3 Atomic number is the number of protons in an atom s nucleus D Bonding 1 Forms a compound with two or more elements 2 Ionic bonds a Atoms giveup or gain valence electrons to form ions 1 Anion negatively charged due to a gain of an electrons 2 Cation positively charged due to a loss of an electronsionic compounds consist of an orderly arrangement of oppositely charged ions 3 Covalent bonds a Atoms share electrons b eg The gaseous elements oxygen Oz and hydrogen H2 4 Other bonds a Both ionic and covalent bonds may occur in the same compound b Metallic bonding 7 valence electrons are free to migrate Isotopes and radioactive decay 1 Mass number the sum of the neutrons plus protons in an atom s nucleus 2 Isotope variants of the same element with more than one mass number 3 Some isotopes have unstable nuclei and emit particles and energy in a process called radioactive decay P1 III Physical properties of minerals A Crystal form 1 External expression of the orderly internal arrangement of atoms 2 Crystal growth is often interrupted because of competition for space B Luster 1 Appearance of re ected light 2 Two basic types a Metallic b Nonmetallic C Color 7391 F I a Often an unreliable diagnostic Property b Varieties of colors 1 Exotic coloration 2 Inherent coloration Streak 1 Color of a mineral in its powdered form 2 Helps to distinguish metallic luster Hardness 1 Resistance of a mineral to abrasion or scratching 2 Mohs scale of hardness Cleavage 1 Tendency to break along planes of weak bonding 2 Described by a Number of planes b Angles at which the planes meet Fracture 1 Absence of cleavage when broken 2 Types a Irregular b Conchoidal Speci c gravity 1 Ratio of the weight of a mineral to the weight of an equal volume of water 2 Can be estimated by hefting the minera Other properties Taste Smell Elasticity Malleability Feel Magnetism Double refraction Reaction to hydrochloric acid WSQM P N Mineral groups A General characteristics 1 Nearly 4000 minerals have been name 2 Rockforming a No more than a few dozen b Make up most of the rocks of Earth s crust 14 CHAPTER 2 c Composed essentially of the eight a Most common member 7 elements that represent over 98 hornblende percent by weight of the b Tetrahedron are arranged in continental crust double chains 1 Oxygen O c Similar in appearance to 2 Silicon Si augite 3 Aluminum Al 4 Biotite mica 4 Iron Fe a Tetrahedron are arranged in 5 Calcium Ca sheets 6 Sodium Na b Excellent cleavage in one 7 Potassium K direction 8 Magnesium Mg b Light nonferromagnesian B Silicate silicates 1 Most common mineral group 1 Muscovite mica 2 Contain siliconoxygen tetrahedron a Light color a Four oxygen ions surrounding a b Excellent cleavage much smaller silicon ion 2 Feldspar b Complex ion with a negative four a Most common mineral 4 charge grou 3 Other silicate structures b Two planes of cleavage a Tetrahedra join to form c Threedimensional 1 Single chains framework of tetrahedron 2 Double chains d Two different varieties of 3 Sheets etc feldspar b Negative structures are neutralized 1 Potassium feldspar by the inclusion of metallic cations 2 Plagioclase sodium and that bond them together calcium feldspar l Ions of the about the same size 3 Quartz are able to substitute freely a Composed entirely of 2 In some cases ions that silicon and oxygen interchange do not have the b Threedimensional same electrical charge framework of tetrahedron 4 Common silicate minerals 4 la a Dark ferromagnesian silicates l Olivine a Hightemperature silicate b Black to olive green in color Glassy luster Conchoidal fracture 2 Pyroxene group a Most common member 7 augite b Tetrahedron are arranged in single chains c Black opaque 3 Amphibole group 99 C a Sheet structure b Term used to describe a variety of complex minerals c Most originate as products of chemical weathering Important nonsilicate minerals 1 Major groups mmngpws Ox1des Sulfates Native elements Carbonates Hydroxides Phosphates Minerals Building Blocks of Rocks V 2 Carbonates B Mineral resources include a Two most common carbonate 1 Reserves 7 already identi ed deposits minerals 2 Known deposits that are not yet 1 Calcite calcium carbonate economically or technologically 2 Dolomite calciummagnesium recoverable carbonate C re b Primary constituents in the 1 A useful metallic mineral that can be sedimentary rocks limestone and mined at a pro t dolostone 2 Must be concentrated above its 3 Halite and gypsum average crustal abundance a Evaporite minerals 3 Pro tability may change because of b Important nonmetallic resources economic changes 4 Many other nonsilicate minerals have 13 The meChanismS that generate igneous economic value a Hematite iron ore b Sphalerite zinc ore c Galena lead ore sedimentary and metamorphic roc s play a major role in producin concentrated accumulations of useful elements Mineral resources A The endowment of useful minerals ultimately available commercially Answers to the Review Questions N 4 U 6 Rocks are aggregates of one or more minerals Protons and neutrons are found in the nucleus and represent practically all of an atom s mass Protons are positively charged whereas neutrons are neutral Electrons orbit the nucleus have practically no mass and carry a negative charge a In a neutral atom the number of protons equals the number of electrons therefore the answer is 35 b The atomic number is the same as the number of protons thus the answer is 35 c By subtracting the number of protons from the mass number the number of neutrons can be determined The number of neutrons is 45 They are the electrons of an atom that are involved in bonding In an ionic bond one or more valence electrons are transferred from one atom to another However in a covalent bond there is a sharing of valence electrons One or more valence electrons are simultaneously gained and lost by atoms participating in a chemical reaction The atoms that gain electrons are negative ions those that lose electrons are positive ions 16 CHAPTER 2 Isotopes of an element have varying numbers of neutrons in the nucleus and hence different atomic weights 00 Usually crystal growth is interrupted because of competition for space The result is an intergrown mass of small closely spaced crystals none of which exhibits its crystal form 0 Impurities often cause the same mineral to have many colors For example uorite can be purple clear yellow etc while quartz can be practically any color O The hardness test might help you make a determination Any mineral listed in Mohs scale corundum for example will scratch softer minerals those with lower hardness values and will not scratch harder minerals Corundum would scratch virtually all other minerals diamond being the lone exception Thus corundum is widely used in abrasives and polishing compounds N The speci c gravity of water is one by de nition Thus equal volumes of water and gold would have their weights in the ratio 120 Since the 25 liters of water weigh 25 kilograms the 25 liters of gold will weigh almost 500 kilograms 25 liters x 20 kgl 500 kg W Silicon is an element The elements silicon and oxygen combine to form the framework of the most common mineral group the silicates All silicate minerals have the siliconoxygen tetrahedron as their fundamental building block This structure consists of four oxygen atoms surrounding a smaller silicon atom 4 Ferromagnesian is a word derived from the chemical elements magnesium and iron ferro ferrous ferric etc The term refers to rock forming silicate minerals that contain some iron Fe andor magnesium Mg in addition to silicon and oxygen Additional elements such as aluminum sodium and calcium may be present without changing the designation Ferromagnesian minerals comprise most of the darkcolored dark green and black mineral grains in igneous rocks U They are both micas with layered sheetsilicate internal crystalline structures and one direction of perfect cleavage Muscovite is the lightcolored potassium aluminum K and Al mica and biotite is the darkercolored ferromagnesian mica contains Mg and Fe 6 No because they both have similar colors The best means of physically distinguishing between the two types of feldspars is to look for ne lines called striations Striations are found on some cleavage planes of plagioclase feldspar but are not present on orthoclase feldspar 1 a hornblende b muscovite c quartz d olivine e plagioclase feldspar f carbonate minerals calcite halite andor gypsum Minerals Building Blocks of Rocks 17 18 Both minerals are carbonates Calcite reacts vigorously with diluted acids such as hydrochloric HCl with the formation of carbon dioxide C02 gas bubbles In contrast dolomite must rst be nely powdered before reacting vigorously enough with the same dilute acid to produce visible bubbling 19 Mineral reserves are identi ed deposits from which minerals can be extracted pro tably The concept of a mineral resource has a broader meaning In addition to including reserves it also includes known deposits that are not yet economically or technologically recoverable as well as deposits that are inferred to exist but not yet discovered 20 One way a mineral deposit could become pro table to extract is through an economic change eg the demand for a metal may increase and cause a price increase Also if a technological advance allows the metal to be extracted at a lower cost it may become pro table to extract and thus be reclassi ed as an ore PowerPoint slides for each chapter of Essentials of Geology accompany the DIGIT disc ISBN 013 008171 X There are instructions in the CD39s ReadMe le for embedding QuickTime for use in the PowerPoint slides For additional resources Visit the Essentials of Geology Home Page at httpwwwprenhallc0mtarbuck 18 CHAPTER 2 NOTES E a S r Freshwater lakes 0009 a lne lakes an in an seas 0 00 39V 8 0 Soil moisture Dn Stream channels a Atrnosphere 0001 Hydrosphere Nonocean Component of total hydrosphere Water Cycle 53gt SGDDDD km1tolalwa1mevapmaled lt If ltXN 268335333quot Evaporalinn r quotw ma 320000 kms PW V R Watersheds Gradient Crosssectional area 10 square umls A Wide shallow Perimeter 12 units channel Crosssectional area 10 square unlts 539 g g mm Per meter 79 units snllullon suspension Oxbow formation Never build on the outside of a River Floodplain Natural Levees Coarse sediments 39 39 Fine sediments v F39Oodplam R V4 Resistant layer Ultimate base level Drainage Patterns A Denunuc Valleys cut in lesswesismnl ck thgs s oi resistant rock or Rectangular Table 101 Fresh water of the hydrosphere 39 L quot L L L Parts of the Volum of Share of Total Volume Rate of Hydrosphere Fresh Water km of Fresh Water percent Water Exchange Ice sheets and glaciers 24000000 84945 8000 years C Groundwater 4000000 14158 280 yea rs Lakes and reservoirs 155000 0549 7 years Soil moisture 83000 0294 1 year W m 1 39 1 eat 5 l we 14000 0049 99 da v 39 39 39 12111022 P 1200 0004 113 Groundwater 1s water found 1n the pores of sod and Total 28253200 1 0000 scdlmcnt plus narrow JO lnts and fractures 1n bedrock Largest reservoir of fresh water that is readily available to humans Erosional agent dissolution of limestone creates sinkholes caves etc karst topography GROUNDWATER The water table Upper limit of the zone of saturation Depth is highly variable varies seasonally and annually smaller or Larger pores Shape is usually a subdued replica of the surface topo particles Factors that contribute to the irregular surface Water tends to pile up beneath high areas Variations in rainfall Variations in permeability GROUNDWATER How groundwater moves Exceedingly slow a few cm per day 0 Energy for movement is powered by gravity 0 Water percolates into a stream from all directions GROUNDWATER Factors in uencing the storage and movement of groundwater Porosity the ability ofa material to store water 0 of the total volume of rock or sediment that consists of pore spaces Determines how much groundwater can be stored Variations can be huge sandstone vs shale Sponge high porosity GROUNDWATER Factors in uencing the storage and movement of groundwater Permeability the ability ofa material to transmit a uid Aquifer permeable rock or sediment that transmits groundwater freely sand gravel Aquitard an impermeable layer that hinders or prevents water from moving clay shale Collander high permeability GROUNDWATER Distribution of underground water 0 Zone of saturation Water reaches a zone where all the open spaces in sediment and rock completely lled with water 0 Water within the pores is called groundwater Zone of aeration Area above the water table 0 Water cannot be pumped by wells Wells Before heavy umping After heavy pumping GROUNDWATER Features associated with groundwater Wells To ensure a continuous supply of water a well must penetrate below the water table Pumping can cause Drawdown lowering of the water table and a Cone of depression in the water table GROUNDWATER Problems associated with groundwater withdrawal Land subsidence Ground sinks when water is pumped from wells faster than natural recharge can replace it Example San Joaquin Valley CA GROUNDWATER Problems associated with groundwater withdrawal Groundwater contamination Sewage is a common source Extremely permeable aquifers coarse gravel have such large openings that groundwater may travel long distances without being cleaned Sewage often becomes purified as it travels through a few dozen meters of an aquifer of sand sandstone GROUNDWATER Problems associated with groundwater withdrawal Groundwater contamination Other sources and types of contamination include Highway salt Fertilizers Pesticides Industrial materials Storage tanks Land lls Holding ponds GROUNDWATER Problems associated with groundwater withdrawal Treating groundwater as a nonrenewable resource In many places the water available to recharge the aquifer falls significantly short of the amount being withdrawn Example The High Plains 5 A 0 meters Interaction between groundwater amp stream Er Losing stream connecxad c Losing stream disconnected GROUNDWATER The water table Interactions between groundwater and streams Gaining streams gain water from the in ow of groundwater through the streambed Losing streams lose water to the groundwater system by out ow through the streambed GROUNDWATER Features associated with groundwater Springs Water table intersects Earth s surface Natural out ow of groundwater Can be caused by an aquitard creating a localized zone of saturation and a perched water table GROUNDWATER Features associated with groundwater Artesian Wells Applied to any situation in which groundwater under pressure rises above the level of the aquifer Types of artesian wells Non owing pressure surface is below ground Flowing pressure surface is above the ground 0 Not all artesian systems are wells springs also omgganasranlye r mu m magi Monuowlng anesi an well WWW suqaca Flowing armsian well Hot springs and geysers Hot springs GROUNDWATER Water is 69 C ll16 F warmer than the mean annua temperature of the locality The water for most is heated by cooling of igneous rock GROUNDWATER Hot springs and geysers Geysers Intermittent hot springs Water erupts with great force Occur Where underground chambers eXist Within hot igneous rock Groundwater heats expands changes to steam erupts Chemical sedimentary rock deposits at the surface Siliceous sinter dissolved silica Travertine dissolved calcium carbonate GROUNDWATER Geothermal energy Tapping natural underground reservoirs of steam and hot water 0 Geothermal energy is not ineXhaustible GROUNDWATER The water table Upper limit of the water table ls called the zone of saturation because it is saturated K fyHydmthsrmalsystemgreatenhan150 C Wlth water I zuna 0V mng anu volcanism GROUNDWATER GROUNDWATER Geologic work of groundwater Geologic work of groundwater Groundwater dissolves rock Caverns Groundwater is mildly acidic contains H2CO3 Most are formed by dissolution at or just below the zone of saturation Carbonic acid reacts with calcite to form calcium bicarbonate a soluble material 0 Zone of aeration Dripstone speleothems Stalactites hang from the ceiling Stalagmites form on the cavern oor build up Sink holes GROUNDWATER Geologic work of groundwater Karst topography Landscapes that to a large extent have been shaped by the dissolving power of groundwater Common features 0 Tower karst GROUNDWATER Geologic work of groundwater Common features 0 Irregular terrain Sinkholes 0 Slowly dissolving bedrock as groundwater moves downward sudden cavern collapse 0 Striking lack of streams Stream piracy Collapse sink GROUNDWATER Geologic work of groundwater T ower karst Southern China 0 Region of steep sided hills 0 Forms in tropical and subtropical regions with thick beds of highly jointed limestone Web phum Szechwan Regmn Suuthem chm Continental Drift Continental drift An o First proposed his continental drift hypothesis in 1915 0 Published The Origin of Continents and Oceans 0 Continental drift hypothesis Supercontinent called Pangaea began breaking apart about 200 million years ago Pangaea approximately 200 Continental drift An million years ago idea before its time gt 48 i 39 0 Continental drift hypothesis f K I o Continents quotdriftedquot to present positions y X 273 quotAg ems 0 Evidence used in support of continental a x V drift hypothesis l O 0 Fit of the continents A 3 0 Fossil evidence g 7 y V f 7 0 Rock type and structural similarities o Paleoclimatic evidence Wegener s matching of mountain The great debate ranges on di rerent continents Objections to the continental drift a p Caledonian MW v 39 39 Mountains W J 39 hypothes1s J J a g Inability to provide a mechanism capable of North 39 QM gg f British moving continents across the globe Americaf I 39S39es 39 It S and ynawa 7r 39 Wegner suggested that contlnents broke Appalachian 39 1 through the ocean crust much like ice 39 jquot139quot39quoti399 ta39ns u o 39 l 39 I 5 breakers cut through ice 1 x Africa South f i America yquot 5 rquot 1139 Paleoclimatic evidence for Continental Drift The great debate Continental drift and the scientific method Wegner s hypothesis was correct in principle but contained incorrect details For any scienti c viewpoint to gain wide acceptance supporting evidence from all realms of science must be found A few scientists considered Wegner s ideas plausible and continued the search Plate tectonics A modern version of an old idea Much more encompass1ng theory than continental drift 0 The composite of a variety of ideas that explain the observed motion of Earth s lithosphere through the mechanisms of subduction and sea oor spreading Plate tectonics A modern version of an old idea 0 Earth s major plates Associated with Earth39s strong rigid outer layer Known as the lithosphere Consists of uppermost mantle and overlying crust Overlies a weaker region in the mantle called the asthenosphere Plate tectonics A modern version of an old idea 0 Earth s major plates Seven major lithospheric plates Plates are in motion and continually changing in shape and size Largest plate is the Paci c plate Several plates include an entire continent plus a large area of sea oor Earth Structure and Plate tectonics n a Fw 2 39 W life gf i lg EH unimam mlEV i a MT t JIMquot DEFUIE39A quot Fl TE N fr 7 Itan l J 7 LL mm H V EweHausaquot 1 1395 V wquot mm 4 wquot 39 w Plate tectonics A modern version of an old idea Plate boundaries 0 All major interactions among individual plates occur along their boundaries 0 Types of plate boundaries 7 Divergent plate boundaries constructive margins 7 Convergent plate boundaries destructive margins 7 Transform fault boundaries conservative margins Plate tectonics A modern version of an old idea Plate boundaries 0 Each plate is bounded by a combination of the three types of boundaries 0 New plate boundaries can be created in response to changes in the forces acting on these rigid slabs Plate Boundaries Plate tectonics A modern version of an old idea Earth s major plates Plates move relative to each other at a very slow but continuous rate 7 Average about 5 centimeters 2 inches per year 7 Cooler denser slabs of oceanic lithosphere descend into the mantle Divergent Plate Boundaries MidAtlantic Ridge System DIVERGENT BOUNDARY Divergent plate boundaries Most are located along the crests of oceanic ridges and can be thought of as constructive plate margins Oceanic ridges and seafloor spreading Along welldeveloped divergent plate boundaries the sea oor is elevated forming oceanic ridges Divergent plate boundaries Oceanic ridges and sea oor spreading Sea oor spreading occurs along the oceanic ridge system Spreading rates and ridge topography Ridge systems exhibit topographic differences Topographic differences are controlled by spreading rates Divergent Plate Boundaries Oceanic ridges and sea oor spreading Longest topographic feature on Earth s surface Represent 20 of Earth s surface 10004000 km wide Create new sea oor Typical spreading rates 5 cm 2 inches per year N0 ocean oor is older than the Jurassic 180 my Divergent boundaries are located Sea oor Spreading Most convincing evidence from ocean drilling Age of deepest sediments Youngest sediments are near the ridges Older sediments are far away from the ridges Con rms sea oorspreading hypothesis Ages show that the ocean basins are geologically young lSubaquatic Continental if Sar Sprain lie 4 Continental Igneous Continental Sedimentary Uceanlc Igneous I Paleozoic 24B 545 Ma and Metamorphic I Jurassic 144 205 Ma IOIigocene 23 34 Ma I Mesozoic 248 65 Ma Preoambrian 545 4550 Ma I Early Cretaceous 144121 Ma lMiocene 5 23 Ma I Cenozoic 65 0 Ma paleozoic 24B 545 Ma I Middle Cretaceous 121 99 Ma IPliocene 2 5 Me I permian 248 290 Ma I Late Cretaceous 99 65 Ma I Pleistocene o 2 Ma Mesozoic 248 65 Ma I Paleocene 65 51 Ma ICenozoic o 55 Ma lCenozoic 65 0 Me Eocene 51 39 31 Ma IMesozoic 65 255 Ma Larson Cande Dewev Golovchenko Divergent plate boundaries Spreading rates and ridge topography Topographic differences are controlled by spreading rates At slow spreading rates 15 centimeters per year a prominent rift valley develops along the ridge crest that is wide 30 to 50 km and deep 15003000 meters At intermediate spreading rates 59 centimeters per year rift valleys that develop are shallow with subdued topography Divergent plate boundaries Spreading rates and ridge topography Topographic differences are controlled by spreading rates At spreading rates greater than 9 centimeters per year no median rift valley develops and these areas are usually narrow and extensively faulted Continental rifts Splits landmasses into two or more smaller segments Divergent plate boundaries Continental rifts Examples include the East African rifts valleys and the Rhine Valley in northern Europe Produced by extensional forces acting on the lithospheric plates Not all rift valleys develop into full edged spreading centers The East African rift a divergent boundary on land 39 Convergent Plate Boundaries Types 1 oceaniccontinental Andes 2 oceanicoceanic Aleutian trench 3 continentalcontinental Himalayas Convergent Plate Boundaries CASCADE RANGE Mt Hood Convergent plate boundaries Older portions of oceanic plates are returned to the mantle in these destructive plate margins Surface expression of the descending plate is an ocean trench Called subduction zones Average angle at Which oceanic lithosphere descends into the mantle is about 45 Convergent plate boundaries 0 Although all have the same basic charac teristics they are highly variable features 0 Types of convergent boundaries Oceaniccontinental convergence 7 Denser oceanic slab sinks into the astheno sphere 0 Types of convergent boundaries Convergent plate boundaries Oceaniccontinental convergence 7As the plate descends partial melting of mantle rock generates magmas having a basaltic or occasionally andesitic composition 7 Mountains produced in part by volcanic activity associated with subduction of oceanic lithosphere are called continental volcanic arcs Andes and Cascades An oceaniccontinental con vergent plate boundary Continental volcanic arc 4 1quot lt7Trench Oceanic crust Convergent plate boundaries 0 Types of convergent boundaries Oceanicoceanic convergence 7When two oceanic slabs converge one descends beneath the other 7 Often forms volcanoes on the ocean floor 7 If the volcanoes emerge as islands a volcanic island arc is formed Japan Aleutian islands Tonga islands An oceanicoceanic convergent plate boundary Volcanic Island arc Convergent plate boundaries 0 Types of convergent boundaries Continentalcontinental convergence 7 Continued subduction can bring two continents together 7 Less dense buoyant continental lithosphere does not subduct 7 Result is a collision between two continental blocks 7 Process produces mountains Himalayas Alps Appalachians A continentalcontinental The collision of India and Asia convergent plate boundary produced the Himalayas 39 r On nsntal 39 Transform Plate Boundaries Transform fault boundaries The third type of plate boundary Plates slide past one another and no new SAN ANDREAS lithosphere is created or destroyed FAULT SYSTEM Transform faults Most join two segments of a midocean ridge as parts of prominent linear breaks in the oceanic crust known as fracture zones Transform fault boundaries Testing the plate tectonics model Paleomagnetism Ancient magnetism preserved in rocks at the TranSfOI39m fallltS time of their formation A few the San Andreas fault and the Alpine fault of New Zealand cut through continental crust Magnetized minerals in rocks Show the direction to Earth s magnetic poles Provide a means of determining their latitude of origin Apparent polarwandering paths Testing the plate tectonics model for Eurasia and North America 0 Paleomagnetism Apparentpoo Polar wandering animal path for Eurasia 500 m y North America path for Eurasia The apparent movement of the magnetic poles 500 4 illustrated in magnetized rocks indicates that the i continents have moved Polar wandering curves for North America and Europe have similar paths but are separated by about 24 of longitude Different paths can be reconciled if the continents are place next to one another Testing the plate tectonics model Testing the plate tectonics model 0 Magnetic reversals and sea oor spreading Magnetic reversals and sea oor spreading Earth39s magnetic eld PeriOdicaHy Verses Geomagnetic reversals are recorded in the polarity the north magnetic pole becomes the south magnetic pole and vice versa Dates when the polarity of Earth s magnetism changed were determined from lava ows ocean crust In 1963 the discovery of magnetic stripes in the ocean crust near ridge crests was tied to the concept of sea oor spreading Paleomagnetic reversals recorded by basalt at midocean ridges Testing the plate tectonics model quot 223 g f 531 Egan g 0 Magnetic reversals and sea oor spreading Paleomagnetism evidence of past magnetism recorded in the rocks was the most convincing evidence set forth to support the concept of sea oor spreading The Pacific has a faster spreading rate than the Atlantic C Period of normal magnetism Testing the plate tectonics model Plate tectonics and earthquakes 0 Plate tectonics model accounts for the global distribution of earthquakes Absence of deepfocus earthquakes along the oceanic ridge is consistent With plate tectonics theory Deepfocus earthquakes are closely associated With subduction zones The pattern of earthquakes along a trench provides a method for tracking the plate39s descent Deepfocus earthquakes occur along convergent boundaries Shallow 1 ntermediate 9 l 3 39 quot 0 Deep quot l 39 39 ill Earthquake foci in the vicinity of the Japan trench Volcanic island arc Trench amp Shallow 0 Intermediate 0 Deep Testing the plate tectonics model Evidence from ocean drilling Some of the most convincing evidence confirming sea oor spreading has come from drilling directly into ocean oor sediment Age of deepest sediments Thickness of ocean oor sediments verifies sea oor spreading Testing the plate tectonics model Hot spots Caused by rising plumes of mantle material Volcanoes can form over them Hawaiian Island chain Most mantle plumes are longlived structures and at least some originate at great depth perhaps at the mantlecore boundary 7 7 7 fixed quotHm Spat The Hawaiian Islands have formed over a stationary hot spot A gt I 1 I Oahu a quot v 9 f 391quot v 39 7 2 2 3 3 Molokai a a g I H ivyv 4 I gt r 49 can 3 Lglands 38 36 1 31 8 i 39 Maui 239 a 3 quotTiquot IeSsthan 10 739 Z r A 7quot AA 1 1 r Digestionng A a H 4 39 45 r a Hot spot flaw 9quot u I a t 7 Hawaii 5 mgtivo nd V 07 toipresent 5 I I 7 27 Oceanic lithosphere Ages given in millions of years Measuring plate motions 0 A number of methods have been em ployed to establish the direction and rate of plate motion Volcanic chains Paleomagnetism Very Long Baseline Interferometry VLBI Global Positioning System GPS Measuring plate motions Calculations show that Hawaii is moving in a northwesterly direction and approaching Japan at 83 centimeters per year A site located in Maryland is retreating from one in England at a rate of about 17 centimeters per year 1O Metamorphism The transition of one rock into another by temperatures andor pressures unlike those in which it formed Metamorphic rocks are produced from Igneous rocks Sedimentary rocks Other metamorphic rocks Metamorphism Metamorphism progresses incrementally from lowgrade to highgrade During metamorphism the rock must remain essentially solid Metamorphic Settings Metamorphic settings Contact or thermal metamorphism driven by a rise in temperature within the host rock Hydrothermal metamorphism chemical alterations from hot ionrich water 39 Regional metamorphism Occurs during mountain building Produces the greatest volume of metamorphic rock Rocks usually display zones of contact andor hydrothermal metamorphism Agents of metamorphism 0 Heat The most important agent Recrystallization results in new stable minerals Two sources of heat Contact metamorphism heat from magma An increase in temperature with depth due to the geothermal gradient Agents of metamorphism Pressure stress Increases with depth Confining pressure applies forces equally in all directions Rocks may also be subjected to differ ential stress which is unequal in different directions Origin of pressure in metamorphism Undeformed strata B Differential stress A ents 0 metamor hism Agents of metamorphism g f p I Chemically active fluids I Chemically active uids I Mainly water with other volatile com I Sources of fluids ponents 7Pore spaces of sedimentary rocks I Enhances migration of ions 7Fracmres in igneous rocks I Aids in recrystallization of existing Hydmwd minerals sud 5 days md mic minera s Agents of metamorphism Metamorphic textures I The importance of parent rock I Texture refers to the size shape and I Most metamorphic rocks have the same arrangement of grains within a rock overall chemical composition as the parent Foliation any planar arrangement of rock from Whlch t ey formed mineral grains or structural features within I Mineral makeup determines to a large a rock extent the degree to which each metamorphic agent will cause change I Examples 0f follatmn 7 Parallel alignment of platy andor elongated minerals M etamorph 1c textures M etamorph 1c textures I Foliation I Foliation I Examples of foliation I Foliation can form in various ways including 7 Parallel alignment of flattened mineral gains 7 Rotation ofplaty andor elongated minerals and pebbles 7 Recrystallization of minerals in the direction of 7 Compositional banding preferred orientation 7 Slaty cleavage where rocks can be easily split into 7 Changing the shape of equidimensional gains thin tabular sheets into elongated shapes that are aligned Development offoliution due to directed pressure Metamorphic textures Foliated textures Rock or slaty cleavage Closely spaced planar surfaces along which rocks split Can develop in a number of ways depending on metamorphic conditions and parent rock Metumorphte textures M etamorphlc textures Foliated textures Foliated textures o Schistosity o Gneissic Platy minerals are discernible with the unaided During higher grades of metamorphism ion eye and exhibit a planar or layered structure migration results in the segregation of minerals Rocks having this texture are referred to as Gneissic rocks exhibit a distinctive banded schist appearance Metumorphte textures M etamorphlc textures Other metamorphic textures Other metamorphic textures 0 Those metamorphic rocks that lack foliation o Porphyroblastic textures are referred to as nonfoliated Large grains called porphyroblasts surrounded Develop in environments where deformation is by a ne39gmined matrix Of Other minerals minimal Porphyroblasts are typically garnet staurolite Typically composed of minerals that exhibit and01 andaluSite equidimensional crystals Common metamorphic rocks Common metamorphic rocks 0 Foliated rocks 0 Foliated rocks 0 Slate Phyllite Very fmegmmed 7 Gradation in the degree of metamorphism E H k 1 between slate and schist 7 xce em me c eavage 7 Platy minerals not large enough to be identi ed 7 Most often generated from lowgrade with the unaided eye metamorphism of shale mudstone or siltstone 7 Glossy Sheen and wavy surfaces 7 Exhibits rock cleavage 7 Composed mainly of fine crystals of muscovite andor chlorite Phyllite left and Slate right lack visible mineral grains C0mm0n metdm0rphic rocks Foliated rocks 0 Schist 7 Medium to coarsegrained 7 Platy minerals predominate 7 Commonly include the micas 7 The term schist describes the texture 7 To indicate composition mineral names are used such as mica schist A mica garnet schist 5 cm Common metamorphic rocks Foliated rocks 0 Gneiss 7 Medium to coarsegrained 7 Banded appearance 7 Highgrade metamorphism 7 Often composed of white or lightcolored feldsparrich layers with bands of dark ferromagnesian minerals Gneiss typically displays a banded appearance Common metamorphic rocks Nonfoliated rocks Marble Coarse crystalline Parent rockwas limestone 0r dolostone Composed essentially of calcite 0r dolomite crystals Used as a decorative and monument stone Exhibits a variety of colors Marble a nonfoliateal metamorphic rock Common metamorphic rocks Nonfoliated rocks Quartzite Formed from a parent rock of quartzrich sandstone Quartz grains are fused together C Grains distorted as ions move rom more stressed to less stressed sites Di Flattened rock ex ttlng distorted quartz grains Quartzite Metamorphic environments Contact or thermal metamorphism Occurs due to a rise in temperature when magma invades a host rock A zone of alteration called an aureole forms in the rock surrounding the magma Most easily recognized When it occurs at the surface or in a nearsurface environment Con tact metamorphism A Implacement of igneous body and metamorphism Metamorphic aureole B Crystallization of pluton Metamorphic environments Hydrothermal metamorphism Chemical alteration caused when hot ion rich uids called hydrothermal solutions circulate through fissures and cracks that develop in rock Most Widespread along the axis of the mid ocean ridge system Metamorphic environments 0 Regional metamorphism Produces the greatest quantity of metamorphic rock Associated with mountain building Regional metamorphism Sedimanls deposited on Sediments deposited on conunsmgl margs oontinanlai margins Metamorphic environments Metamorphic environments ther metamorphic environments 0 Impact metamorphism 7 Occurs when high speed projectiles called meteorites strike Earth s surface 7 Products are called impactites Other metamorphic environments 0 O Burial metamorphism 7 Associated with very thick sedimentary strata 7 Required depth varies from one location to another depending on the prevailing geothermal gradient Metamorphism along fault zones 7 Occurs at depth and high temperatures 7 Preexisting minerals deform by ductile ow Metamorphic rocks and associated environments M etamOI phic zones o H 5 0 Systematic variations in the mineralogy and often the textures of metamorphic rocks are related to the variations in the degree of metamorphism Index minerals and metamorphic grade 0 Changes in mineralogy occur from regions of lowgrade metamorphism to regions of high grade metamorphism 1 Metamorphic zones in the M etamOrPhlc Zones North eastern United States 200 Index minerals and metamorphic grade 0 Certain minerals called index minerals are good indicators of the metamorphic conditions in which they form Migmatites 7 Highest grades of metamorphism that is transitional to igneous rocks 7 Contain light bands of igneous components along with areas of umnelted metamorphic rock kilometers Key E Not metamorphosed Low F Chlorile zone grade Biotile zone Medium 1 Gamer zone grade Staurolile zone 952 i Sinimanixe zone lexlnn Comment Excauam rock cteavaga mm dull mm Breaks al wave m 23 main Woman minerals m cuminre analy re ulion W Camposniamal handl mm saw two numerals Banded rock Mm lanes av Irgmwored avaraurne minerah Bedd llg planes wnan very rim graham Marni chad alien braaks imoslabs Stretched pehm wllh prelde urienlalian Imavlncwng calcite or dolom s grain Fused quartz grains a massive very hard may dark mmlva rock with dull iustar Shiny black rack that may mm cameras rectum Brommgmems In a haphazard Antwanm A Uniform pressure B Differential stress B Differential stress